Multilayer mirror, method for manufacturing the same, and exposure equipment

ABSTRACT

A multilayer mirror aims to reduce incidence angle dependence of reflectivity. A substrate is made of low thermal polished expansion glass with 0.2 nm RMS or less roughness of the surface. On the surface thereof formed is a Ru/Si multilayer having a wide full-width half maximum of peak reflectivity, and on the Ru/Si multilayer formed is a Mo/Si multilayer having a high peak reflectivity value. This enables higher reflectivity than when Ru/Si alone provided and a reflectivity peak having a wider full-width half maximum than when the Mo/Si multilayer alone provided. Since Ru absorbs EUV ray more than Mo does, higher reflectivity is obtainable than that of a structure having the Ru/Si multilayer formed on the Mo/Si multilayer. The multilayer with a wide full-width half maximum has small incidence angle dependence of reflectivity in spectral reflectivity, thereby achieving high imaging performance in projection optical system.

CROSS REFERENCE TO RELATED APPLICATION

This is a Divisional of application Ser. No. 11/907,798 filed Oct. 17,2007, which is a Divisional of application Ser. No. 11/401,946 filedApr. 12, 2006 which is a Continuation of International ApplicationPCT/JP2004/015284 filed Oct. 15, 2004, designating the U.S., and claimsthe benefit of priority from Japanese Patent Application Nos.2003-354561, 2003-354568, and 2003-354989, all filed on Oct. 15, 2003,and No. 2004-094633, filed on Mar. 29, 2004, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE PRIOR ART

1. Technical Field

The present invention relates to a multilayer mirror etc. used in EUVlithography and, more particularly, to a technique for reducing theincidence angle dependence of the reflectivity on the surface of amirror.

2. Background of the Prior Art

At present, as a method for manufacturing a semiconductor integratedcircuit, reduced projection exposure capable of obtaining a highprocessing speed is widely utilized. In the reduced projectiontechnique, as the semiconductor integrated circuit device becomes morefiner, projection lithography using soft X-rays having a wavelength ofabout 11 to 14 nm instead of ultraviolet ray is being developed (referto non-patent document 1). Recently, the technique is also called as theEUV (Extreme Ultra-Violet, soft X-ray) lithography. The EUV lithographyis expected as a technique having a resolution of 45 nm or less, whichhas been impossible to realize with the conventional photolithography (awavelength of about 190 nm or more).

Meanwhile, in a currently mainstream reduced projection optical systemusing visible or ultraviolet ray, a lens, which is a transmission typeoptical element, can be used. A reduced projection optical system forwhich a high resolution is required is composed of a number of lenses.In contrast to this, in the wavelength band of the EUV ray (soft X-ray),there is no transparent material and the refractive index of a materialis very close to 1, therefore, a conventional optical element making useof refraction cannot be used. Instead of this, a grazing incidencemirror making use of total reflection, a multilayer mirror capable ofobtaining a high reflectivity as a whole by aligning the phase of weakreflected light at the boundary surface to overlap a number of reflectedlight rays, etc., are used.

In a projection optical system using a lens, it is possible to realizean optical system in which light advances in one direction along theoptical axis, however, in a projection optical system configured by amirror, a flux of light is turned back many times. Due to this, itbecomes necessary to prevent the turned back flux of light frominterfering with a mirror substrate spatially and the numerical aperture(NA) in the optical system is restricted.

At present, as a projection optical system, ones composed of four to sixmirrors are proposed. In order to attain a sufficient resolution, it ispreferable for the numerical aperture of a projection optical system tobe large, therefore, an optical system composed of six mirrors capableof attaining a large numerical aperture is considered to be promising.As an example of six-mirror optical system, there is a configurationproposed by Takahashi et al. (refer to the patent document 1 and FIG. 21to be described later).

In order for a reduced projection optical system to exhibit sufficientperformance in reduced projection exposure, the configuration of anillumination optical system is also important. In order for a projectionoptical system to exhibit a sufficient resolution, it is necessary forirradiation intensity to be uniform in a pupil as well as illuminatingan exposure region on a mask on which a circuit pattern to betransferred is formed with uniform intensity.

Further, in order to secure throughput, it is also important toilluminate with the light as strong as possible. As an example of suchan illumination optical system, which is disclosed in, for example, thepatent document 2.

In the multilayer mirror constituting an EUV optical system, materialssuited to obtain a high reflectivity differ depending on the wavelengthband of incidence light. For example, in the wavelength band near 13.5nm, if a molybdenum Mo/Si multilayer in which a molybdenum (Mo) layerand a silicon (Si) layer are laminated by turns is used, a reflectivityof 67.5% can be obtained for vertical incidence. Further, in thewavelength band near 11.3 nm, if a Mo/Be multilayer in which amolybdenum (Mo) layer and a beryllium (Be) layer are laminated by turnsis used, a reflectivity of 70.2% can be obtained for vertical incidence(refer to the non-patent document 2). The full width at half maximum(FWHM) of the reflectivity peak of the multilayer reported in thenon-patent document 2 is about 0.56 nm in the case of the Mo/Simultilayer the periodic length of which has been adjusted so as to havea peak at a wavelength of 13.5 nm for vertical incidence.

Meanwhile, it is known that the reflectivity of a multilayer mirrorvaries considerably depending on the optical incidence angle andwavelength. FIG. 19 is a graph showing an example of the incidence angledependence of the reflectivity of a conventional multilayer mirror. Inthe drawing, the horizontal axis represents the incidence angle (degree(°)) of the light that is made incident into a multilayer mirror and thevertical axis represents the reflectivity (%) for the EUV ray with awavelength (λ) of 13.5 nm. As seen from the drawing, in the conventionalmultilayer mirror, a high reflectivity of 70% or more is obtained whenthe incidence angle is about 0° to 5°, however, when it is 10° or more,the reflectivity falls considerably.

FIG. 20 is a graph showing an example of the spectral reflectivityproperties of a conventional multilayer mirror. In the drawing, thehorizontal axis represents the wavelength (λ) of the incidence light andthe vertical axis represents the reflectivity (%). Note that, theincidence angle is assumed to be 0° (vertical incidence to thereflective surface). As seen from the drawing, in the conventionalmultilayer mirror, a high reflectivity of 70% or more is obtained in thevicinity of a wavelength of 13.5 nm (in the central part in thedrawing), however, in other wavelength bands other than that, thereflectivity falls considerably.

For such a problem, Kuhlmann et al. has proposed a reflective multilayerhaving an approximately uniform reflectivity across a wide wavelengthband by making uneven the periodic structure (film thickness of eachlayer) of the reflective multilayer (refer to the non-patent document3). The non-patent document 3 discloses a structure of a multilayerhaving a wide band for the reflectivity angle distribution or thespectral reflectivity, which has been obtained by adjusting thethickness of each layer of a 50-layer pair multilayer using acommercially available multilayer optimizing program.

For example, in the case of a multilayer the periodic length of which isconstant, if the periodic length is optimized such that the reflectivityis maximum in a vertical incidence arrangement, the range in which ahigh reflectivity can be kept is when the incidence angle is 0° to 5°and when the incidence angle is 10° or more, the reflectivity fallsconsiderably. In contrast to this, the non-patent document 3 discloses amultilayer having an uneven structure in film thickness, thereflectivity of which becomes almost constant at about 45% in theincidence angle range of 0° to 20°. Although the full width at halfmaximum (FWHM) of the spectral reflectivity peak of a normal Mo/Simultilayer is about 0.56 nm, the non-patent document 3 also discloses astructure the reflectivity of which becomes almost uniform at 30% acrossthe wavelength range of 13 nm to 15 nm for vertical incidence.

The uniformization of the reflectivity in a wide wavelength band and theuniformization in a wide incidence angle range described above are notthe properties that can be controlled individually, and in a multilayercapable of obtaining a uniform reflectivity in a wide wavelength band,there is a trend that the change in reflectivity becomes small even in awide incidence angle range. A multilayer capable of obtaining a uniformreflectivity in such a wide wavelength range can make use of the EUV rayin a wide wavelength region although the reflectivity peak value islower than that of a normal multilayer, therefore, it can be expected tobe capable of obtaining a large amount of light depending on itsapplications when the band of the incidence light wavelength is wide.

Further, Singh et al. have reported that by making the ┌ value (theproportion of the periodic length of a multilayer to the thickness of aMo layer) uneven in the depth direction in a Mo/Si multilayer, thereflectivity is increased (refer to the non-patent document 4). The EUVreflectivity of a Mo/Si multilayer reaches its maximum when the ┌valueis 0.35 to 0.4, however, the non-patent document 4 discloses that a moreincrease in reflectivity can be obtained when bringing the ┌value ofMo/Si close to 0.5 at the portion of the substrate side (deep layerside) of the multilayer than when setting it to a constant value of 0.4for the entire multilayer.

Meanwhile, as a configuration of a reflective multilayer capable ofobtaining a high reflectivity for the EUV ray in the vicinity of awavelength of 13 nm, Ru/Si is known, in addition to Mo/Si (Ru stands forruthenium). If it is assumed that n is a refractive index and k is anextinction coefficient (the imaginary part of a complex refractiveindex), the optical constants (n, k) of silicon at a wavelength of 13.5nm are

n (Si)=0.9993, and

k (Si)=0.0018.

In contrast to this, the optical constants (n, k) of molybdenum andruthenium are

n (Mo)=0.9211,

k (Mo)=0.0064,

n (Ru)=0.8872, and

k (Ru)=0.0175,

respectively.

Like a multilayer for the EUV ray, when absorption occurs in themultilayer itself, in order to obtain a high reflectivity, it ispreferable that the difference in refractive index of a substanceconstituting the multilayer be large and absorption be small. As seenfrom the above-mentioned optical constants, from the standpoint ofrefractive index, a Ru/Si multilayer is suited and from the standpointof absorption, a Mo/Si is more suited to obtain a high reflectivity. Inthe case of these two multilayers, the influence of absorption isdominant and the Mo/Si multilayer has a higher peak reflectivity.

The full width at half maximum of the reflectivity peak of a multilayeris brought about by the difference in refractive index. It is known thatthe band full width (2Δg) of the peak of the reflectivity of adielectric multilayer (a multilayer in which two substances havingdifferent refractive indices are laminated by turns) well known ininfrared, visible, and ultraviolet regions is expressed by the followingformula (for example, refer to non-patent document 5).

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack & \; \\{{2\Delta \; g} = {\frac{4}{\pi} \cdot {\sin^{- 1}\left( \frac{n_{H} - n_{L}}{n_{H} + n_{L}} \right)}}} & (1)\end{matrix}$

Here, n_(H) is the refractive index of a high refractive-index substanceand n_(L) is the refractive index of a low refractive-index substance.

As seen from the above formula, the larger the refractive indexdifference between the two substances constituting a multilayer, themore the band increases, therefore, a wider full width at half maximumcan be obtained from a Ru/Si multilayer than that from a Mo/Simultilayer. In the case where there is no absorption by a film, the peakvalue of the dielectric multilayer reflectivity gradually reaches 100%,however, in the EUV region it does not reach 100% because of absorption.

Since the magnitude of absorption depends on the wavelength, if thechange in reflectivity versus wavelength is plotted, the reflectivity isasymmetry before and after the peak wavelength. The peak reflectivity ofa multilayer in the EUV region increases as the number of pairs offormed films increases, however, it saturates at a certain number ofpairs. The number of pairs with which saturation is reached is about 50pair layers for a Mo/Si multilayer and about 30 pair layers for a Ru/Simultilayer. The reason that the reflectivity reaches saturation is thatby reflection and absorption at each boundary surface when the EUV raypasses through a film, almost no light reaches a position deeper thanthat and there is no longer contribution to the reflection of the entirefilm. A Ru/Si multilayer is greater than a Mo/Si multilayer in themagnitude of absorption and the reflectivity at a single boundarysurface is higher, therefore, the number of pairs with which saturationis reached is smaller.

REFERENCES

-   Patent document 1: Japanese Unexamined Patent Application    Publication No. 2003-15040-   Patent document 2: Japanese Unexamined Patent Application    Publication No. 11-312638-   Non-patent document 1: Daniel A. Tichenor, and other 21 persons,    “Recent results in the development of an integrated EUVL laboratory    tool”, Proceedings of SPIE, (USA), (SPIE, The International Society    for Optical Engineering), May 1995, Vol. 2437, p. 293-   Non-patent document 2: Claude Montcalm, and other five persons,    “Multilayer reflective coatings for extreme-ultraviolet    lithography”, Proceedings of SPIE, (USA), (SPIE, The international    Society for Optical Engineering), June, 1989, Vol. 3331, p. 42-   Non-patent document 3: Thomas Kuhlmann, and other three persons,    “EUV multilayer mirrors with tailored spectral reflectivity”,    Proceedings of SPIE, (USA), (SPIE, The International Society for    Optical Engineering”, 2003, Vo. 4782, p. 196-   Non-patent document 4: Mandeep Singh, and other one person,    “Improved Theoretical Reflectivities of Extreme Ultraviolet    Mirrors”, Proceedings of SPIE, (USA), July, 2000, Vol. 3997, p. 412-   Non-patent document 5: written by H. A. Macleod, translated by    Shigetaro Ogura and other three persons, “Thin-film optical    filters”, The Nikkan Kogyo Shimbun, Ltd., November, 1989

PROBLEM TO BE SOLVED BY THE INVENTION

A projection optical system actually used in EUV lithography is composedof a multilayer mirror, in which a Mo/Si multilayer is formed on asubstrate.

FIG. 21 shows an example of a projection optical system composed of sixmirrors. The projection optical system is composed of six mirrors CM1 toCM6 and light reflected by a mask M is projected onto a wafer W. Thefour mirrors CM1 to CM4 on the upstream side (the side nearer to themask M) in the optical system constitute a first reflection imageforming optical system G1 for forming an intermediate image of a maskpattern on the mask M, and the two mirrors CM5 and CM6 on the downstreamside (the side nearer to the wafer W) constitute a second reflectionimage forming optical system G2 for performing reduced projection of anintermediate image of a mask pattern onto the wafer W.

The light reflected by the mask M is reflected by a reflective surfaceR1 of a first concave mirror CM1 and reflected by a reflective surfaceR2 of a second convex mirror CM2.

The light reflected by the reflective surface R2 passes through anaperture diaphragm AS and after reflected by a reflective surface R3 ofa third convex mirror CM3 and a reflective surface R4 of a fourthconcave mirror sequentially, forms an intermediate image of a maskpattern. Then, the light from the intermediate image of the mask patternformed via the first reflection image forming optical system G1 isreflected by a reflective surface R5 of a fifth convex mirror CM5 and areflective surface R6 of a sixth concave mirror CM6, then forms areduced image of the mask pattern on the wafer W.

The periodic length distribution in the substrate plane of a Mo/Simultilayer formed on the surface of a mirror directly affects thereflectivity distribution in the plane and the in-plane distribution ofthe reflectivity affects the image forming performance as the in-planeilluminance variations on the formed image surface or the light amountvariations in the pupil plane, therefore, it is necessary to establishan optimum in-plane distribution by taking all of them intoconsideration. However, since it is difficult to form a film on asubstrate with a free film thickness distribution, therefore, it isgeneral to optimize with an axis-symmetric film thickness distributionaround the optical axis of an optical system when the optical system isconfigured.

Even if the periodic length distribution is optimized as describedabove, there still remains a problem as described below. In theprojection optical system shown in FIG. 21, the light that reaches apoint on the image forming surface does not come only from one directionto reach the image forming surface, but it comes from a solid anglespace having a certain extent to converge to a point. In other words, abundle of rays that contribute to image formation at a point on theimage forming surface are reflected in a region on each mirror substratehaving a finite area and two regions on the mirror substratecorresponding to two points not so apart from each other on the imageforming surface partially overlap each other. In other words, reflectionat a single point on the mirror substrate contributes to image formationin a region having a certain extent on the image forming surface and therays reflected at the same point reach different points on the imageforming surface. At this time, the rays reaching different points on theimage forming surface are made incident to the same point on the mirrorat different angles and therefore, an incidence angle at a certain pointon the reflective surface has a certain extent.

In a multilayer mirror, the optimum periodic length for a fixedwavelength depends on the incidence angle, therefore, in a strict sense,an optimum periodic length for all incidence angles is not available. Ifthe extent of the incidence angle is not so large, its influence is notlarge. However, even if the periodic length in-plane distribution of anormal Mo/Si multilayer (the periodic length is constant) is optimizedfor a mirror substrate constituting an optical system, for example, asshown in FIG. 21, such that the wave surface aberration of thetransmitted light becomes smaller, large variations in the lightintensity in the pupil plane occur. Here, the distribution of themultilayer periodic length is optimized in a range of an axis-symmetricdistribution around the optical axis at the time of configuration of anoptical system under the restriction of the film forming methoddescribed above.

The variations in light intensity in the pupil plane is opticallyequivalent to that the effective NA becomes smaller irregularly,therefore, the image forming performance is degraded considerably. Thisis a problem that occurs in a normal Mo/Si multilayer because theincidence angle dependence of the reflectivity is large. Because ofthis, a method has been demanded that reduces the incidence angledependence of the reflectivity on a mirror surface that degrades theimage forming performance and that attains high image formingperformance.

Further, in order to attain high image forming performance in aprojection optical system, it is necessary for the illumination lightintensity distribution on a mask and the light intensity distribution inthe pupil plane in an illumination optical system to be uniform. This isbecause the light intensity distribution in the pupil plane in anillumination optical system is reflected directly in the intensitydistribution on an image forming surface and the intensity distributionin the pupil plane in a projection optical system.

Furthermore, in a multilayer mirror in an illumination optical systemcurrently proposed, the in-plane distribution of incidence angle islarge. Because of this, it is difficult to strictly match the optimumperiodic length at all of the points on a reflective surface. This isbecause the amount of change in the in-plane periodic lengthdistribution needs to be increased and since a slight shift is producedwhen the periodic length distribution is controlled at the time of filmformation or when alignment as an illumination optical system isperformed, the film thickness corresponding to a supposed incidenceangle differs from the film thickness corresponding to an actualincidence angle and considerable degradation in the reflectivity isbrought about. In this case, there is a problem of decrease in theamount of light that can be used for illumination and reduction in thethroughput. There has been a demand for a technique for reducing theincidence angle dependence of the reflectivity on the mirror surface.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a technique forreducing the incidence angle dependence of the reflectivity on amultilayer mirror etc.

According to a first embodiment of the present invention, a multilayermirror has a reflective multilayer in which a high refractive-index filmand a low refractive-index film for the EUV ray are laminated by turnsand has the following features. First, in the multilayer (the surfacelayer film group) on the light incidence plane side, the lowrefractive-index film is composed of a substance including molybdenum(Mo) and the high refractive-index film is composed of a substanceincluding silicon (Si). Second, in the multilayer (deep layer filmgroup) on an opposite light incidence plane side of the surface layerfilm group, the low refractive-index film is composed of a substanceincluding ruthenium (Ru) and the high refractive-index film is composedof a substance including silicon.

Here, the high refractive-index film or the low refractive-index filmmay be a single layer or a composite layer in which a plurality oflayers are overlapped. Further, another layer may be interposed betweenthe high refractive-index film and the low refractive-index film.

According to the present invention, a substance including molybdenumalso includes, for example, rhodium (Rh), carbon (C), silicon (Si), etc.In other words, a substance including molybdenum may be molybdenumincluding Rh, C, and Si as impurities or may be a compound of thesesubstances and molybdenum (this similarly applies to a substanceincluding ruthenium and a substance including silicon). Further, asubstance including ruthenium also includes, for example, rhodium (Rh),carbon (C), silicon (Si), etc. Furthermore, a substance includingsilicon also includes, for example, carbon (C), carbon tetraboride(B₄C), boron (B), etc.

According to the first embodiment described above, the Mo/Si multilayerhaving a high peak value of reflectivity is formed on the Ru/Simultilayer having a large full width at half maximum of the reflectivitypeak, so that it is possible to obtain the reflectivity higher than thatin the case of only Ru/Si, and a reflectivity peak with a wider fullwidth at half maximum than that in the case of only the Mo/Simultilayer. Further, Ru absorbs EUV ray more than Mo does, therefore, ahigher reflectivity is obtained than that in a structure in which theRu/Si multilayer is formed on the Mo/Si multilayer. A multilayer havinga wide full width at half maximum with respect to the spectralreflectivity has less incidence angle dependence of the reflectivitywhich makes it possible to keep high image forming performance of aprojection optical system according to the present invention.

According to a first embodiment, it is preferable for the number ofpairs of a high refractive-index film and a low refractive-index film inthe surface layer film group to be 2 to 10. The number of laminations ofthe Mo/Si multilayer is 10 or less, so that the full width at halfmaximum of the reflectivity peak is kept wide due to the influence fromRu/Si formed on the substrate side. Further, the uppermost surface isthe Mo/Si multilayer having a higher reflectivity than that of the Ru/Simultilayer, therefore, the peak reflectivity increases. This makes itpossible to obtain a multilayer having a high reflectivity and a widefull width at half maximum, which cannot be otherwise attained with theMo/Si multilayer or the Ru/Si multilayer alone.

The multilayer mirror in the first embodiment is manufactured by thefollowing method. In other words, it is only necessary for the method tohave a process for forming a deep layer film group by alternatelydepositing a substance including ruthenium and a substance includingsilicon on a substrate and a process for forming a surface layer filmgroup by alternately depositing a substance including molybdenum and asubstance including silicon on the deep layer film group.

According to a second embodiment of the present invention, a multilayermirror has a reflective multilayer in which a high refractive-index filmand a low refractive-index film for EUV ray are laminated by turns andhas the following features. First, it has a multilayer film group (asurface layer film group) on the light incidence plane side, anadditional layer on the opposite incidence plane side in the surfacelayer film group, and a multilayer film group (a deep layer film group)on the opposite incidence plane side of the additional layer. Second,the reflected light is shifted in phase due to the presence of theadditional layer, so that the reflectivity peak value is reduced in themirror as a whole, and at the same time, the reflectivity around peakwavelengths is increased compared to the case where no additional layeris present.

According to a third embodiment of the present invention, a multilayermirror has a reflective multilayer in which a high refractive-index filmand a low refractive-index film for EUV ray are laminated by turns andhas the following features. First, it has a multilayer film group (asurface layer film group) on the light incidence plane side, anadditional layer on the opposite incidence plane side in the surfacelayer film group, and a multilayer film group (a deep layer film group)on the opposite incidence plane side in the additional layer. Second, inthe surface layer film group, the low refractive-index film is composedof a substance including ruthenium (Ru) and the high refractive-indexfilm is composed of a substance including silicon (Si). Third, in thedeep layer film group, the low refractive-index film is composed of asubstance including ruthenium (Ru) and the high refractive-index film iscomposed of a substance including silicon. Fourth, the thickness of theadditional layer is about half the periodic length of the multilayer orthe thickness of about half the periodic length plus an integer multipleof the periodic length. Note that the low refractive-index film in thesurface layer film group may be composed of a substance includingmolybdenum (Mo) instead of a substance including ruthenium (Ru) asdescribed above. Further, the low refractive-index film in the deeplayer film group may also be composed of a substance includingmolybdenum (Mo) instead of ruthenium.

In the multilayer mirror in the second and third embodiments describedabove, it is preferable for the number of unit periodic structures(pairs) of the surface layer film group to be 10 to 30 and for thenumber of pairs of the deep layer film group to be 5 to 50% of thenumber of pairs of the surface layer film group.

In the multilayer mirror in the second and third embodiments, theadditional layer is provided at the position of from the tenth period tothe thirtieth period from the uppermost surface of the multilayer,however, EUV ray reaches a position deeper than the additional layer.Therefore, the reflected light from the multilayer film group (the deeplayer film group) on the opposite incidence plane side (the substrateside) of the additional layer contributes to the reflectivity of theentire multilayer.

The phase of the reflected light from the periodic multilayer above andunder the additional layer (the incidence plane side and the oppositeincidence plane side) shifts in the vicinity of the reflectivity peakdue to the thickness of the additional layer, therefore, the amplitudeof the reflected light attenuates. Because of this, the reflectivitydecreases at the front end portion of the reflectivity peak due to thepresence of the additional layer. The reflectivity peak shape in themultilayer the number of pairs of which is less than that with which thereflectivity saturates is a shape the top of which is pointed, however,as the reflectivity of the peak portion decreases, the top portion ofthe peak approaches a flat shape (the peak portion comes to bear broadproperties).

On the other hand, the situation differs considerably at the portion ofthe foot apart from the peak. In a normal periodic structure, when thewavelength is shifted from the optimized wavelength (the wavelength atwhich the reflectivity peak is obtained), a shift in the phase is smallin the reflected light from the boundary surface in the vicinity of thesurface, therefore, the amplitude increases by overlapping each other,however, there may be a case where the phase of the reflected light fromthe boundary surface apart from the surface turns into the oppositephase to attenuate the amplitude. At the wavelengths corresponding tothe foot of the reflectivity peak of the Mo/Si or Ru/Si multilayer, thereflected light from the boundary surface after the tenth pair layer tothe thirtieth pair layer acts so as to reduce the reflected lightintensity. However, if the additional layer is added, the phase of thereflected light from the boundary surface at a position deeper than thatshifts by half the wavelength, therefore, the amplitude of the reflectedlight increases.

As described above, by providing an additional layer between the surfacelayer film group and the deep layer film group, the front end portion ofthe reflectivity peak is flattened and at the portion of the foot of thereflectivity, the reflectivity increases, therefore, the full width athalf maximum of the reflectivity peak increases. In the case of theRu/Si multilayer or the Mo/Si multilayer, in the wavelength range from12 to 15 nm, a reflectivity exceeding 60% is obtained theoretically. Byadapting the multilayer structure according to the present invention tothese multilayers, it is possible to obtain a multilayer having areflectivity the full width at half maximum of which is wider than thatof Ru/Si and Mo/Si without an additional layer.

Also, in the multilayer mirror in the second and third forms describedabove, the additional layer may be made of silicon (Si), boron (B), or asubstance including these. The extinction coefficient k of silicon (Si)and boron (B) at a wavelength of 13.5 nm is as relatively small as

k (Si)=0.0018, and

k (B)=0.0041

The role of the additional layer is to shift the phase of the reflectedlight in the deep layer film group and the surface layer film group by ½wavelength, therefore, preferably the absorption is as small as possibleand a higher reflectivity can be attained by using these substances or asubstance (for example, B₄C) including these substances.

According to a fourth embodiment of the present invention, a multilayermirror has a reflective multilayer in which a high refractive-index filmand a low refractive-index film for EUV ray are laminated by turns andhas the following features. First, it is provided with a multilayer filmgroup (a surface layer film group) on the light incidence plane side, anadditional layer on the opposite incidence plane side of the surfacelayer film group, and a multilayer film group (a deep layer film group)on the opposite incidence plane side of the additional layer. Second, inthe multilayer film group (a first surface layer film group) on theincidence plane side of the surface layer film group, the lowrefractive-index film is composed of a substance including molybdenum(Mo) and the high refractive-index film is composed of a substanceincluding silicon (Si). Third, in the multilayer film group (a secondsurface layer film group) on the additional layer side of the surfacelayer film group, the low refractive-index film is composed of asubstance including ruthenium (Ru) and the high refractive-index film iscomposed of a substance including silicon (Si). Fourth, in the deeplayer film group, the low refractive-index film is composed of asubstance including ruthenium (Ru) and the high refractive-index film iscomposed of a substance including silicon.

According to the fourth embodiment described above, a multilayercomposed of molybdenum and silicon is formed on the multilayer of astructure in which the additional layer is added to the substantiallyperiodic multilayer composed of ruthenium and silicon. Even the Ru/Simultilayer of the periodic structure can have a full width at halfmaximum wider than that of the Mo/Si multilayer, and even the multilayerhaving the additional layer added can have a full width at half maximumwider than that of the Mo/Si multilayer. By forming a Mo/Si filmthereon, the peak value of the peak reflectivity can be increased and awider full width at half maximum can be obtained.

According to a fifth embodiment of the present invention, a multilayermirror has a reflective multilayer in which a high refractive-index filmand a low refractive-index film are laminated on a substrate by turnsunder a condition that a Bragg's reflection condition holds thatreflected light from a plurality of boundary surfaces of the highrefractive-index film and low refractive-index film for EUV ray is putin phase and has the following features. First, it includes aninterposed layer whose thickness is half or more of the centerwavelength of EUV ray. Second, the band of the EUV ray wavelength orincidence angle having a relatively high EUV ray reflectivity iswidened.

According to the fifth embodiment described above, part of a pair ofhigh refractive-index film and low refractive-index film (layer pair) iscomposed of two kinds of substances and another part thereof may becomposed of three or more kinds of substances.

Further, in the fifth embodiment, the reflective multilayer may includea plurality of blocks in which a pair (layer pair) of a highrefractive-index film H and low refractive-index films L1 and L2 havingdifferent structures are laminated repeatedly. For example, a block inwhich a layer pair of L1/L2/L1/H is repeated and a block in which alayer pair of L1/H is repeated may be included, and the number ofrepetitions of the layer pair lamination in each block may be 1 to 50.In this case, the film thickness of a layer included in each layer pairmay differ in each layer pair. Note that, it is assumed that the filmconstituting substances of L1 and L2 are different from each other (thisapplies hereinafter). Further, in the fifth embodiment, it may also bepossible to perform lamination while varying the film thickness of eachfilm arbitrarily and set the reflectivity for the light with awavelength of 13.1 nm to 13.9 nm to 45% or more.

According to a sixth embodiment of the present invention, a multilayermirror has a reflective multilayer in which a high refractive-index filmand a low refractive-index film are laminated on a substrate by turnsunder a condition that a Bragg's reflection condition holds thatreflected light from a plurality of boundary surfaces of the highrefractive-index film and low refractive-index film for EUV ray is putin phase and has the following features. First, the reflectivemultilayer includes a plurality of blocks in which a pair (layer pair)of a high refractive-index film H and low refractive-index films L1 andL2 having different structures are laminated repeatedly. Second, a blockon the substrate side of the multilayer mirror is formed by repeatedlylaminating a layer pair of L2/H, the second block from the substrate isformed by repeatedly laminating a layer pair of L2/L1/H, the third blockfrom the substrate is formed by repeatedly laminating a layer pair ofL1/H, the fourth block from the substrate is formed by repeatedlylaminating a layer pair of L1/L2/L1/H, the fifth block from thesubstrate is formed by repeatedly laminating a layer pair of L2/L1/H,the sixth block from the substrate is formed by repeatedly laminating alayer pair of L1/H, the seventh block from the substrate is formed byrepeatedly laminating a layer pair of L1/L2/L1/H, and the eighth blockfrom the substrate is formed by repeatedly laminating a layer pair ofL1/H. Third, the number of repetitions of the layer pair lamination ineach block is 1 to 50. Fourth, the band of the EUV ray wavelength orincidence angle having a relatively high EUV ray reflectivity iswidened.

Note that, in the sixth embodiment, it is preferable for thereflectivity to be 50% or more for the light at grazing incidence madeincident at an incidence angle at least in a range from 18 degrees to 25degrees. It is preferable for an incidence angle range including adesired angle (for example, 20 degrees) in an incidence angle range of 0to 25 degrees to be within five degrees, or more preferably within sevendegrees of an incidence angle range, in which the reflectivity is 50% ormore, and in which the reflectivity peak has a flat shape (thefluctuation in the reflectivity is within ±5%).

According to a seventh embodiment of the present invention, a multilayermirror has a reflective multilayer in which a high refractive-index filmand a low refractive-index film are laminated on a substrate by turnsunder a condition that a Bragg's reflection condition holds thatreflected light from a plurality of boundary surfaces of the highrefractive-index film and low refractive-index film for EUV ray is putin phase and has the following features. First, the reflectivemultilayer includes a plurality of blocks in which a pair (layer pair)of a high refractive-index film H and low refractive-index films L1 andL2 having different structures are laminated repeatedly. Second, theblock on the substrate side of the multilayer mirror is formed byrepeatedly laminating a layer pair of L2/H, the second block from thesubstrate is formed by repeatedly laminating a layer pair of L2/L1/H,the third block from the substrate is formed by repeatedly laminating alayer pair of L1/H, the fourth block from the substrate is formed byrepeatedly laminating a layer pair of L2/L1/H, the fifth block from thesubstrate is formed by repeatedly laminating a layer pair of L1/L2/L1/H,the sixth block from the substrate is formed by repeatedly laminating alayer pair of L1/H, the seventh block from the substrate is formed byrepeatedly laminating a layer pair of L1/L2/L1/H, and the eighth blockfrom the substrate is formed by repeatedly laminating a layer pair ofL1/H. Third, the number of repetitions of the layer pair lamination ineach block is 1 to 50. Fourth, a band of EUV ray wavelength or incidenceangle having a relatively high EUV ray reflectivity is widened.

According to the seventh embodiment, it is possible to uniformalize thereflectivity on the entire reflective surface by arbitrarily varying thetotal film thickness of the reflective multilayer in accordance with theincidence angle of light at each position on the reflective surface.Further, in the seventh embodiment, it is possible to set thereflectivity to 50% or more for the light at grazing incidence madeincident at an incidence angle at least in the range from 0 to 20degrees by varying the total film thickness of the reflective multilayerwhile maintaining the ratio of the film thickness of each layer in thereflective multilayer.

According to an eighth embodiment of the present invention, a multilayermirror has a reflective multilayer in which a high refractive-index filmand a low refractive-index film are laminated on a substrate by turnsunder a condition that a Bragg's reflection condition holds thatreflected light from a plurality of boundary surfaces of the highrefractive-index film and low refractive-index film for EUV ray is putin phase and has the following features. First, the reflectivemultilayer includes a plurality of blocks in which a pair (layer pair)of a high refractive-index film H and low refractive-index films L1 andL2 having different structures are laminated repeatedly. Second, theblock on the substrate side of the multilayer mirror is formed byrepeatedly laminating a layer pair of L1/L2/L1/H, the second block fromthe substrate is formed by repeatedly laminating a layer pair ofL2/L1/H, the third block from the substrate is formed by repeatedlylaminating a layer pair of L1/L2/L1/H, the fourth block from thesubstrate is formed by repeatedly laminating a layer pair of L2/L1/H,the fifth block from the substrate is formed by repeatedly laminating alayer pair of L1/H, the sixth block from the substrate is formed byrepeatedly laminating a layer pair of L1/L2/L1/H, the seventh block fromthe substrate is formed by repeatedly laminating a layer pair ofL2/L1/H, the eighth block from the substrate is formed by repeatedlylaminating a layer pair of L1/L2/L1/H, the ninth block from thesubstrate is formed by repeatedly laminating a layer pair of L1/H, thetenth block from the substrate is formed by repeatedly laminating alayer pair of L1/L2/L1/H, the eleventh block from the substrate isformed by repeatedly laminating a layer pair of L2/L1/H, the twelfthblock from the substrate is formed by repeatedly laminating a layer pairof L1/L2/L1/H, and the thirteenth block from the substrate is formed byrepeatedly laminating a layer pair of L1/H. Third, the number ofrepetitions of the layer pair lamination in each block is 1 to 50.Fourth, the band of the EUV ray wavelength or incidence angle having arelatively high EUV ray reflectivity is widened. According to the eighthembodiment, it is preferable for the reflectivity for the light atgrazing incidence made incident at an incidence angle at least in therange from 0 to 20 degrees to be 45% or more.

According to a ninth embodiment of the present invention, a multilayermirror has a reflective multilayer in which a high refractive-index filmand a low refractive-index film are laminated on a substrate by turnsunder a condition that a Bragg's reflection condition holds thatreflected light from a plurality of boundary surfaces of the highrefractive-index film and low refractive-index film for EUV ray is putin phase and has the following features. First, the reflectivemultilayer includes a plurality of blocks in which a pair (layer pair)of a high refractive-index film H and low refractive-index films L1 andL2 having different structures are laminated repeatedly. Second, theblock on the substrate side of the multilayer mirror is formed byrepeatedly laminating a layer pair of L2/H, the second block from thesubstrate is formed by repeatedly laminating a layer pair of L2/L1/H,the third block from the substrate is formed by repeatedly laminating alayer pair of L2/H, the fourth block from the substrate is formed byrepeatedly laminating a layer pair of L1/H, the fifth block from thesubstrate is formed by repeatedly laminating a layer pair of L2/H, thesixth block from the substrate is formed by repeatedly laminating alayer pair of L2/L1/H, the seventh block from the substrate is formed byrepeatedly laminating a layer pair of L1/H, the eighth block from thesubstrate is formed by repeatedly laminating a layer pair of L2/L1/H,the ninth block from the substrate is formed by repeatedly laminating alayer pair of L1/H, the tenth block from the substrate is formed byrepeatedly laminating a layer pair of L2/L1/H, the eleventh block fromthe substrate is formed by repeatedly laminating a layer pair of L1/H,the twelfth block from the substrate is formed by repeatedly laminatinga layer pair of L2/L1/H, the thirteenth block from the substrate isformed by repeatedly laminating a layer pair of L1/L2/L1/H, and thefourteenth block from the substrate is formed by repeatedly laminating alayer pair of L1/H. Third, the number of repetitions of the layer pairlamination in each block is 1 to 50. Fourth, the band of the EUV raywavelength or incidence angle having a relatively high EUV rayreflectivity is widened. According to the ninth embodiment, it ispreferable for the reflectivity for the light having a wavelength of13.1 nm to 13.9 nm to be 45% or more.

According to a tenth embodiment of the present invention, a multilayermirror has a reflective multilayer in which a high refractive-index filmand a low refractive-index film are laminated on a substrate by turnsunder a condition that a Bragg's reflection condition holds thatreflected light from a plurality of boundary surfaces of the highrefractive-index film and low refractive-index film for EUV ray is putin phase and has the following features. First, the reflectivemultilayer includes a plurality of blocks in which a pair (layer pair)of a high refractive-index film H and low refractive-index films L1 andL2 having different structures are laminated repeatedly. Second, theblock on the substrate side of the multilayer mirror is formed of alayer of H, the second block from the substrate is formed by repeatedlylaminating a layer pair of L2/H, and the third block from the substrateis formed by repeatedly laminating a layer pair of L2/L1/H. Third, thenumber of repetitions of the layer pair lamination in each block is 1 to50. Fourth, the band of the EUV ray wavelength or incidence angle havinga relatively high EUV ray reflectivity is widened.

According to an eleventh embodiment of the present invention, amultilayer mirror has a reflective multilayer in which a highrefractive-index film and a low refractive-index film are laminated on asubstrate by turns under a condition that a Bragg's reflection conditionholds that reflected light from a plurality of boundary surfaces of thehigh refractive-index film and low refractive-index film for EUV ray isput in phase and has the following features. First, at least one layerof the high refractive-index films has a thickness of half or more ofthe center wavelength of the EUV ray. Second, the band of the EUV raywavelength or incidence angle having a relatively high EUV rayreflectivity is widened.

The exposure equipment of the present invention is exposure equipmentfor forming a pattern by selectively irradiating a sensitive substratewith EUV ray and having the above-mentioned multilayer mirror in anoptical system. According to the exposure equipment of the presentinvention, a multilayer with a wide band is formed at least at a part inthe projection optical system and the illumination optical system,therefore, it is possible to make uniformalize the illuminance on theimage forming surface and the in-pupil light amount and to keep highimage forming performance. Further, it is possible to prevent the dropin light amount caused by the alignment error of a mirror with a largeperiodic length in-plane distribution in the projection optical system.

With the multilayer mirror of the present invention, it is possible toobtain reflectivity peak properties the reflectivity of which isrelatively high and having a wide full width at half maximum. Since amultilayer having a wide full width at half maximum of spectralreflectivity has small incidence angle dependence of reflectivity,according to the present invention, it is possible to keep high theimage forming performance in a projection optical system.

Since the exposure equipment of the present invention uses such amultilayer mirror, it is possible to uniformalize the illuminance on theimage forming surface and the in-pupil light amount and to keep highimage forming performance.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature, principle, and utility of the invention will become moreapparent from the following detailed description when read inconjunction with the accompanying drawings in which like parts aredesignated by identical reference numbers, in which:

FIG. 1 is a sectional view showing a multilayer mirror according to afirst embodiment of the present invention;

FIGS. 2(A), (B) show the calculated values of reflectivity of themultilayer mirror according to the first embodiment of the presentinvention as the dependence on the wavelength of incidence light;

FIGS. 3(A), (B) show the calculated values of reflectivity of themultilayer mirror according to the first embodiment of the presentinvention as the dependence on the incidence angle of incidence light;

FIG. 4 is a sectional view showing a multilayer mirror according to asecond embodiment of the present invention;

FIGS. 5 (A), (B) show the calculated values of reflectivity of themultilayer mirror according to the second embodiment of the presentinvention, wherein (A) shows the dependence on the wavelength ofincidence light and (B) shows dependence on the incidence angle ofincidence light;

FIG. 6 is a sectional view showing a multilayer mirror according to athird embodiment of the present invention;

FIGS. 7 (A), (B) show the calculated values of reflectivity of themultilayer mirror according to the third embodiment of the presentinvention, wherein (A) shows the dependence on the wavelength ofincidence light and (B) shows dependence on the incidence angle ofincidence light;

FIG. 8 is a sectional view showing a multilayer mirror according to afourth embodiment of the present invention;

FIGS. 9 (A), (B) show the calculated values of reflectivity of themultilayer mirror according to the fourth embodiment of the presentinvention, wherein (A) shows the dependence on the wavelength ofincidence light and (B) shows dependence on the incidence angle ofincidence light;

FIG. 10 shows the incidence angle dependence of the reflectivity of amultilayer mirror according to a fifth embodiment of the presentinvention;

FIGS. 11(A) to (H) show the incidence angle dependence of thereflectivity of a multilayer mirror according to a sixth embodiment ofthe present invention;

FIGS. 12 (A) to (F) show the incidence angle dependence of thereflectivity of the multilayer mirror according to the sixth embodimentof the present invention;

FIG. 13 shows the incidence angle dependence of the reflectivity of amultilayer mirror according to a seventh embodiment of the presentinvention;

FIG. 14 shows the spectral reflectivity properties of a multilayermirror according to an eighth embodiment of the present invention;

FIG. 15 shows the spectral reflectivity properties of a multilayermirror according to a ninth embodiment of the present invention;

FIG. 16 shows the spectral reflectivity properties of a multilayermirror according to a tenth embodiment of the present invention;

FIG. 17 shows the incidence angle dependence of the reflectivity of themultilayer mirror according to the seventh embodiment of the presentinvention;

FIG. 18 is a schematic diagram showing exposure equipment according toan embodiment of the present invention;

FIG. 19 shows an example of the incidence angle dependence of thereflectivity of a conventional multilayer mirror;

FIG. 20 shows an example of the spectral reflectivity properties of aconventional multilayer mirror;

FIG. 21 shows an example of an optical system configured by six mirrors;

FIG. 22(A) shows the incidence wavelength properties of the theoreticalreflectivity of a Mo/Si multilayer and a Ru/Si multilayer and FIG. 22(B) shows the change in the full width at half maximum and peakreflectivity for the number of formed pair layers of the Mo/Simultilayer in a multilayer formed by forming the Mo/Si multilayer filmon the Ru/Si multilayer film;

FIG. 23 shows a reflectivity peak shape when the thickness of anadditional layer (a silicon layer) is varied against the periodic lengthof a Mo/Si multilayer;

FIG. 24 is a diagram schematically showing a structure of an Etalon;

FIGS. 25(A) to (C) show expected diffraction peak shapes of aperiodically structured multilayer, an uneven periodic structure, and amultilayer including an additional layer, respectively when the X-raydiffraction intensity angle distribution is varied; and

FIG. 26 shows the change in the reflectivity peak shape of a Mo/Simultilayer when the number of pairs of a deep layer film group isvaried.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, there will be described embodiments of the presentinvention with reference to the accompanying drawings.

Embodiment 1

FIG. 1 is a sectional schematic diagram of a multilayer mirror accordingto a first embodiment of the present invention. A substrate 1 is made oflow thermal expansion glass polished until the roughness of the surface(the upper surface in the drawing) is 0.2 nm RMS or less. On the surfaceof the substrate 1, 20 pair layers of Ru/Si multilayer 3 are formed andon the Ru/Si multilayer 3, five pair layers of Mo/Si multilayer 5 areformed. The periodic length (the thickness of unit periodic structure(layer pair) of Ru/Si, denoted by d₁₁ in the drawing) of the Ru/Simultilayer 3 is 6.86 nm and the periodic length (the thickness of thelayer pair of Mo/Si, denoted by d₁₂ in the drawing) of the Mo/Simultilayer 5 is 6.9 nm. The r value of these multilayers is 0.4 in eachunit periodic structure. Note that, the ┌ value is a ratio (┌=d_(Ru)/d,or ┌=d_(Mo)/d) of the thickness (d_(Ru), or d_(Mo)) of the Ru layer orMo layer to the periodic length (d) of the multilayer.

Here, a method for manufacturing a multilayer in the present embodimentis explained. First, the surface of the substrate 1 made of low thermalexpansion glass is polished until 0.2 nm RMS or less is attained. Next,on the surface of the substrate 1, 20 pair layers of Ru/Si multilayer 3are formed by magnetron sputtering. Then, on the surface of the Ru/Simultilayer 3, five pair layers of Mo/Si multilayer 5 are formed bymagnetron sputtering.

FIG. 2 and FIG. 3 are graphs showing the calculated values ofreflectivity of the multilayer mirror according to the presentembodiment. FIG. 2(A) and FIG. 2(B) show the dependence on thewavelength of incidence light and FIG. 3(A) and FIG. 3(B) show thedependence on the incidence angle of incidence light. The horizontalaxis in FIG. 2 represents the wavelength of incidence light. Thehorizontal axis in FIG. 3 represents the incidence angle (hereinafter,the incidence angle refers to an angle that the incidence light makeswith the normal to the reflective surface). In both drawings, thevertical axis represents the reflectivity of the multilayer and thesolid line (i) indicates the reflectivity of the multilayer (the deeplayer side: 20 pair layers of Ru/Si, the surface layer side: five pairlayers of Mo/Si). The dotted line (ii) in FIG. 2(A) and FIG. 3(A) andthe dotted line (iii) in FIG. 2(B) and FIG. 3(B) are comparativeexamples. The comparative example (ii) shows the reflectivity of theRu/Si multilayer of 26 pair layers and the comparative example (iii)shows the reflectivity of the Mo/Si multilayer of 2 pair layers.

As shown in FIG. 2(A), the reflectivity peak value of the multilayer (i)in the present embodiment is 69.7% and the full width at half maximum is0.86 nm. In contrast to this, in the comparative example (ii) (the Ru/Simultilayer of 26 pair layers), like the present embodiment (i), the fullwidth at half maximum is as wide as 0.86 nm, however, the reflectivitypeak value is as low as 67.4%, which is lower by 2% or more. Further, asshown in FIG. 2(B), in the comparative example (iii) (the Mo/Simultilayer of 27 pair layers), the peak value is about 70.0%, which issubstantially the same as the present embodiment (i), however, the fullwidth at half maximum is 0.72 nm, narrower by 0.1 nm or more. Asdescribed above, by forming the Mo/Si multilayer on the Ru/Simultilayer, a reflectivity the peak value of which is high and the fullwidth at half maximum of which is wide can be obtained.

As shown in FIG. 3(A), the multilayer (i) in the present embodimentresembles the comparative example (ii) in that the reflectivity ismaximum and almost constant in the incidence angle range of 0° to 10°,however, the peak reflectivity is higher than that in the comparativeexample (ii). Further, as shown in FIG. 3(B), the peak reflectivity ofthe multilayer (i) in the present embodiment is higher than that in thecomparative example (iii) and the incidence angle range in which thepeak reflectivity thereof is constant is wider than that in thecomparative example (iii). As described above, in the presentembodiment, a reflectivity that is almost constant in a wide incidenceangle range can be obtained.

Note that, the periodic length referred to in the present embodiment isjust an example, and the periodic length may be adjusted in accordancewith the target wavelength to be used. Further, in the presentembodiment, the multilayer is formed by magnetron sputtering, however,the film forming method is not limited to this and a film may be formedby ion beam sputtering or vacuum deposition. In the present embodiment,the ┌ value of the multilayer is set to 0.4, however, the ┌ value is notlimited to this and the ┌ value may be increased to, for example, about0.5 on the substrate if the periodic structure can be controlled. Inthis case, a higher reflectivity can be obtained (refer to thenon-patent document 4 described above).

Embodiment 2

FIG. 4 is a sectional schematic diagram of a multilayer mirror accordingto a second embodiment of the present invention. A substrate 10 is madeof low thermal expansion glass polished until the roughness of thesurface (the upper surface in the drawing) is 0.2 nm RMS or less. On thesurface of the substrate 10, four pair layers of Mo/Si multilayer (deeplayer film group) 11 are formed. The periodic length of the Mo/Simultilayer 11 (the thickness of the pair layer of Mo/Si) is 6.9 nm andthe ┌ value is 0.5.

On the surface of the Mo/Si multilayer 11, an additional layer 12 (inthe present embodiment, a silicon layer) is formed. The thickness of theadditional layer 12 is adjusted so as to have an optical thickness ofabout one-fourth of the wavelength of incidence light. In the presentembodiment, the thickness of the additional layer 12 is about 3.5 nm.Further, on the surface of the additional layer 12, 20 pair layers ofMo/Si multilayer (surface layer film group) 13 having a periodic lengthof 6.9 nm and a ┌ value of 0.4 are formed. Additionally, in the drawing,the surface layer film group 13 and the deep layer film group 11 arefurther simplified and shown.

FIG. 5 is a graph showing the calculated values of reflectivity of themultilayer mirror according to the present embodiment. FIG. 5(A) showsthe dependence on the wavelength of incidence light and FIG. 5(B) showsthe dependence on the incidence angle of incidence light.

The horizontal axis in FIG. 5(A) represents the wavelength of incidencelight and the horizontal axis in FIG. 5(B) represents the incidenceangle. In both drawings, the vertical axis represents the calculatedvalues of the reflectivity. The solid line (W1) in the drawing indicatesthe reflectivity of the multilayer mirror in the present embodiment andthe dotted line (C) shows a comparative example. The comparative example(C) shows the reflectivity of the Mo/Si multilayer of 40 pair layers.

As shown in FIG. 5(A), the full width at half maximum of thereflectivity peak of the multilayer (W1) in the present embodiment is0.9 nm or more. Further, the shape of the reflectivity peak in thepresent embodiment (W1) is a top-flattened shape and the reflectivity isabout 52%, almost constant, in the wavelength range of 13.2 nm to 13.7nm. When this is compared to the comparative example (C), the peak valueof the reflectivity of the multilayer (W1) in the present embodiment isnot a match for that in the comparative example (C), which is amultilayer of a simple periodic structure, however, it is known that theuniformity in the reflectivity across a wide wavelength band is veryexcellent.

As shown in FIG. 5(B), the reflectivity of the multilayer (W1) in thepresent embodiment is almost constant across a wide range of theincidence angle of 0° to about 13°.

In contrast to this, in the comparative example (C), the incidence anglerange in which the reflectivity is almost constant is 0° to about 7°. Inthe present embodiment, the range in which the reflectivity is constantis obviously wider than that in the comparative example (C). Therefore,according to the present embodiment, the incidence angle dependence ofthe reflectivity is considerably reduced and it is known that a highreflectivity can be obtained in a wide incidence angle range.

Supplementary items of the embodiment 2 are explained below. In thepresent embodiment, the ┌ value of the multilayer is varied between theupper part and the lower part of the additional layer 12, however, thepresent invention is not limited to this and for example, the ┌ valuemay be the same. Further, in the present embodiment, silicon is used asthe material of the additional layer 12, however, the material of theadditional layer is not limited to this. As the material of theadditional layer, in addition to silicon, boron (B), Mo, and Ru theabsorption in the EUV region is small, or carbon tetraboride (B₄C),silicon carbide (SiC), etc., including these substances are preferable.If a slight drop in the reflectivity does not bring about a seriousproblem, other substances will do. However, even in a case where any oneof the substances is used, it is necessary for the thickness, theoptical thickness, of the additional layer 12 to be about one-fourth ofthe wavelength of incidence light (about half the multilayer periodiclength) or the thickness plus an integer multiple of the periodiclength. The above-mentioned supplementary items also apply toembodiments 3 and 4.

In the present embodiment, with the additional layer 12 sandwiched inbetween, the four pair layers are formed on the substrate side and the20 pair layers are formed on the incidence side, however, the number ofpairs is not limited to this. It is desirable to vary the number ofpairs so as to obtain an adequate reflectivity or a uniform reflectivityin accordance with the purpose of use.

Embodiment 3

FIG. 6 is a sectional schematic diagram of a multilayer mirror accordingto a third embodiment of the present invention. A substrate 20 is madeof low thermal expansion glass polished until the roughness of thesurface (the upper surface in the drawing) is 0.2 nm RMS or less. On thesurface of the substrate 20, five pair layers of Ru/Si multilayer (deeplayer film group) 21 are formed. The periodic length of the Ru/Simultilayer 21 (the thickness of the pair layer of Ru/Si) is 6.9 nm andthe ┌ value is 0.5.

On the surface of the Ru/Si multilayer 21, an additional layer 22 (inthe present embodiment, a silicon layer) is formed. The thickness of theadditional layer 22 is adjusted so as to have an optical thickness ofabout one-fourth of the wavelength of incidence light. In the presentembodiment, the thickness of the additional layer 22 is about 3.85 nm.Further, on the surface of the additional layer 22, 20 pair layers ofRu/Si multilayer (surface layer film group) 23 having a periodic lengthof 6.96 nm and a ┌ value of 0.4 are formed.

FIG. 7 is a graph showing the calculated values of reflectivity of themultilayer mirror according to the present embodiment. FIG. 7(A) showsthe dependence on the wavelength of incidence light and FIG. 7(B) showsthe dependence on the incidence angle of incidence light. The horizontalaxis in FIG. 7(A) represents the wavelength of incidence light and thehorizontal axis in FIG. 7(B) represents the incidence angle. In bothdrawings, the vertical axis represents the calculated values of thereflectivity. The solid line (W2) in the drawing indicates thereflectivity of the multilayer mirror in the present embodiment and thedotted line (C) shows a comparative example. The comparative example (C)shows the reflectivity of the Mo/Si multilayer of 40 pair layers.

As shown in FIG. 7(A), the full width at half maximum of thereflectivity peak of the multilayer (W2) in the present embodiment is1.0 nm or more. Further, the shape of the reflectivity peak in thepresent embodiment (W2) is a top-flattened shape and the reflectivity isabout 60%, almost constant, in the wavelength range of 13.2 nm to 13.7nm. When this is compared to the comparative example (C), the peak valueof the reflectivity of the multilayer (W2) in the present embodiment isnot a match for that in the comparative example (C), which is amultilayer of a simple periodic structure, however, it is known that theuniformity in the reflectivity across a wide wavelength band is veryexcellent.

As shown in FIG. 7(B), the reflectivity of the multilayer (W2) in thepresent embodiment is almost constant across a wide range of theincidence angle of 0° to about 13°.

In contrast to this, in the comparative example (C), the incidence anglerange in which the reflectivity is almost constant is 0° to about 7°.Therefore, in the present embodiment, the range in which thereflectivity is constant is obviously wider than that in the comparativeexample (C). Thus, in the present embodiment, the incidence angledependence of the reflectivity is considerably reduced and it is knownthat a high reflectivity can be obtained in a wide incidence anglerange.

Note that, in the present embodiment, with the additional layer 22sandwiched in between, the five pair layers are formed on the substrateside and the 20 pair layers are formed on the incidence side, however,the number of pairs is not limited to this. It is desirable to vary thenumber of pairs so as to obtain an adequate reflectivity or a uniformreflectivity in accordance with the purpose of use.

Embodiment 4

FIG. 8 is a sectional schematic diagram of a multilayer mirror accordingto a fourth embodiment of the present invention. A substrate 30 is madeof low thermal expansion glass polished until the roughness of thesurface (the upper surface in the drawing) is 0.2 nm RMS or less. On thesurface of the substrate 30, five pair layers of Ru/Si multilayer (deeplayer film group) 31 are formed. The periodic length of the Ru/Simultilayer 31 (the thickness of the pair layer of Ru/Si) is 6.96 nm andthe ┌ value is 0.5.

On the surface of the Ru/Si multilayer 31, an additional layer 32 (inthe present embodiment, a silicon layer) is formed. The thickness of theadditional layer 32 is adjusted so as to have an optical thickness ofabout one-fourth of the wavelength of incidence light.

In the present embodiment, the thickness of the additional layer 32 isabout 3.75 nm. Further, on the surface of the additional layer 32, 16pair layers of Ru/Si multilayer (second surface layer film group) 33having a periodic length of 6.96 nm and a F value of 0.4 are formed, andon the surface of the Ru/Si layer 33, five pair layers of Mo/Simultilayer (first surface layer film group) 34 having a periodic lengthof 6.9 nm and a ┌ value of 0.4 are formed.

FIG. 9 is a graph showing the calculated values of reflectivity of themultilayer mirror according to the present embodiment. FIG. 9(A) showsthe dependence on the wavelength of incidence light and FIG. 9(B) showsthe dependence on the incidence angle of incidence light.

The horizontal axis in FIG. 9(A) represents the wavelength of incidencelight and the horizontal axis in FIG. 9(B) represents the incidenceangle. In both drawings, the vertical axis represents the calculatedvalues of the reflectivity, the solid line (W3) indicates thereflectivity of the multilayer mirror in the present embodiment, and thedotted line (C) shows a comparative example. The comparative example (C)shows the reflectivity of the Mo/Si multilayer of 40 pair layers.

As shown in FIG. 9(A), the full width at half maximum of thereflectivity peak of the multilayer (W3) in the present embodiment is1.0 nm or more. Further, the shape of the reflectivity peak in thepresent embodiment (W3) is a top-flattened shape and the reflectivity isabout 62%, almost constant, in the wavelength range of 13.2 nm to 13.7nm. When this is compared to the comparative example (C), the peak valueof the reflectivity of the multilayer (W3) in the present embodiment isnot a match for that in the comparative example (C), which is amultilayer of a simple periodic structure, however, it is known that theuniformity in the reflectivity across a wide wavelength band is veryexcellent.

As shown in FIG. 9(B), the reflectivity of the multilayer (W3) in thepresent embodiment is almost constant across a wide range of theincidence angle of 0° to about 10° and the reflectivity does not dropconsiderably up to an incidence angle of about 15°. In contrast to this,in the comparative example (C), the incidence angle range in which thereflectivity is almost constant is 0° to about 7°, and the reflectivitysharply drops in the vicinity of the incidence angle of about 10°.Therefore, in the present embodiment, the range in which thereflectivity is constant is obviously wider than that in the comparativeexample (C). Thus, in the present embodiment, the incidence angledependence of the reflectivity is considerably reduced and it is knownthat a high reflectivity can be obtained in a wide incidence anglerange.

Note that, in the present embodiment, with the additional layer 32sandwiched in between, the five pair layers are formed on the substrateside and the 21 (=16+5) pair layers are formed on the incidence side,however, the number of pairs is not limited to this. It is desirable tovary the number of pairs so as to obtain an adequate reflectivity or auniform reflectivity in accordance with the purpose of use.

Embodiment 5

Next, a multilayer mirror according to a fifth embodiment of the presentinvention will be explained. In the multilayer in the presentembodiment, the material configuration and the film thickness of eachlayer are optimized by using the Needle Method so as to be capable ofobtaining a uniformly high reflectivity for the EUV ray (ExtremeUltra-Violet ray) having a wavelength of 13.5 nm and being made incidentat an incidence angle of 15° to 25°.

The multilayer in the present embodiment is one formed on the surface ofa synthetic silica glass substrate precisely polished, including aplurality of blocks in which a layer pair (a unit periodic structure)having different structures is laminated repeatedly. Here, a layer pair(a unit periodic structure) is one in which a low refractive-index filmmade of a substance having a low refractive index and a highrefractive-index film made of a substance having a high refractive indexfor EUV ray are laminated into a multilayer. In the present embodiment,molybdenum (Mo) and ruthenium (Ru) are used as a low refractive-indexfilm and silicon (Si) is used as a high refractive-index film.

Additionally, in the following explanation, the configuration of amultilayer is expressed by the configuration of one layer pair in eachblock (unit periodic structure) and the number of laminated layer pairs(the number of repetitions) and each block is expressed by a numbercounted from the substrate (the A-th block).

The configuration of the multilayer in the present embodiment is shownin Table 1. The total film thickness of the multilayer in the presentembodiment is about 450 nm. Further, it is preferable for the thicknessof each layer of the multilayer to be not constant and to be adjusted soas to obtain a desired reflectivity by varying in accordance with theposition on the multilayer.

TABLE 1 A Unit Periodic Structure Number of Repetitions 1 Ru/Si 3 2Ru/Mo/Si 4 3 Mo/Si 6 4 Mo/Ru/Mo/Si 1 5 Ru/Mo/Si 4 6 Mo/Si 20 7Mo/Ru/Mo/Si 14 8 Mo/Si 4 9 Mo 1

In the following Table 2, Table 3, and Table 4, the film thickness ofeach layer of the multilayer in the present embodiment is shown. Inthese tables, each layer of the multilayer is expressed by a numbercounted from the substrate side and a preferable film thickness range(nm) and a more preferable film thickness (nm) are shown for each layer.Note that, since the number of layers of the multilayer is large, thetable is shown in a plurality of divided tables.

TABLE 2 Unit Preferable Film More Preferable Periodic Thickness RangeFilm Thickness Structure (nm) (nm)  1 Ru 6~2 4  2 Si 6~2 4  3 Ru 6~2 4 4 Si 6~2 4  5 Ru 6~2 4  6 Si 6~2 4  7 Ru 5~2 3  8 Mo 2~0 1  9 Si 6~2 410 Ru 4~1 3 11 Mo 2~0 1 12 Si 6~2 4 13 Ru 4~1 2 14 Mo 2~0 1 15 Si 6~2 416 Ru 3~1 2 17 Mo 3~1 2 18 Si 6~2 4 19 Mo 5~2 3 20 Si 6~2 4 21 Mo 4~1 222 Si 6~2 4 23 Mo 2~0 1 24 Si 6~2 4 25 Mo 5~2 3 26 Si 6~2 4 27 Mo 5~2 428 Si 6~2 4 29 Mo 5~2 4 30 Si 6~2 4 31 Mo 2~0 1 32 Ru 2~0 1 33 Mo 3~1 234 Si 6~2 4 35 Ru 3~1 2 36 Mo 2~0 2 37 Si 6~2 4 38 Ru 3~1 2 39 Mo 3~1 240 Si 6~2 4 41 Ru 2~0 2 42 Mo 3~1 2 43 Si 6~2 4 44 Ru 2~0 1 45 Mo 4~1 246 Si 6~2 4 47 Mo 5~2 3 48 Si 6~2 4 49 Mo 5~2 3 50 Si 7~2 4 51 Mo 4~1 352 Si 7~2 5 53 Mo 3~1 2 54 Si 25~8  17 55 Mo 3~1 2 56 Si 7~2 5 57 Mo 4~13 58 Si 7~2 4 59 Mo 5~2 3 60 Si 6~2 4 61 Mo 5~2 3 62 Si 6~2 4 63 Mo 5~23 64 Si 6~2 4 65 Mo 5~2 3 66 Ru 6~2 4 67 Mo 5~2 3 68 Si 6~2 4

TABLE 3 More Unit Preferable Preferable Periodic Film Thickness FilmThickness Structure Range(nm) (nm) 69 Mo 5~2 3 70 Si 6~2 4 71 Mo 5~2 372 Si 6~2 4 73 Mo 5~2 3 74 Si 7~2 4 75 Mo 5~2 3 76 Si 7~2 5 77 Mo 4~1 378 Si 8~3 5 79 Mo 3~1 2 80 Si 35~12 23 81 Mo 4~1 3 82 Si 7~2 5 83 Mo 5~23 84 Si 6~2 4 85 Mo 5~2 3 86 Si 6~2 4 87 Mo 2~0 1 88 Ru 2~0 1 89 Mo 3~12 90 Si 6~2 4 91 Mo 2~0 1 92 Ru 3~1 2 93 Mo 2~0 1 94 Si 6~2 4 95 Mo 2~01 96 Ru 3~1 2 97 Mo 2~0 1 98 Si 6~2 4 99 Mo 2~0 1 100  Ru 3~1 2 101  Mo2~0 1 102  Si 6~2 4 103  Mo 2~0 1 104  Ru 3~1 2 105  Mo 2~0 1 106  Si6~2 4 107  Mo 2~0 1 108  Ru 3~1 2 109  Mo 2~0 1 110  Si 6~2 4 111  Mo2~0 1 112  Ru 3~1 2 113  Mo 2~0 1 114  Si 6~2 4 115  Mo 2~0 1 116  Ru3~1 2 117  Mo 2~0 1 118  Si 6~2 4 119  Mo 2~0 1 120  Ru 3~1 2 121  Mo2~0 1 122  Si 6~2 4 123  Mo 2~0 1 124  Ru 3~1 2 125  Mo 2~0 2 126  Si6~2 4

TABLE 4 Unit Preferable Film More Preferable Periodic Thickness FilmThickness Structure Range(nm) (nm) 127 Mo 2~0 1 128 Ru 2~0 2 129 Mo 2~02 130 Si 6~2 4 131 Mo 2~0 1 132 Ru 2~0 1 133 Mo 3~1 2 134 Si 6~2 4 135Mo 2~0 1 136 Ru 2~0 1 137 Mo 3~1 2 138 Si 6~2 4 139 Mo 2~0 1 140 Ru 2~01 141 Mo 3~1 2 142 Si 6~2 4 143 Mo 5~2 3 144 Si 6~2 4 145 Mo 5~2 3 146Si 6~2 4 147 Mo 5~2 3 148 Si 7~2 4 149 Mo 5~2 3 150 Si 7~2 4 151 Mo 4~13

According to the table, the silicon layers of the 54th and 80th layerscounted from the substrate side are thicker than other layers (in thefollowing explanation, these are referred to as extremely thick siliconlayers). The extremely thick silicon layer has a thickness of half ormore of the center wavelength of EUV ray and serves a role as aninterposed layer for widening the band of the EUV ray wavelength orincidence angle having a relatively high EUV ray reflectivity byadjusting the phase difference of the EUV ray reflected from theboundary surface of each layer.

FIG. 10 is a graph showing the incidence angle dependence of thereflectivity of the multilayer mirror according to the presentembodiment. In the drawing, the horizontal axis represents the incidenceangle (degree (°)) of light made incident to the multilayer mirror andthe vertical axis represents the reflectivity (%) for the EUV ray havinga wavelength (λ) of 13.5 nm. As seen from the drawing, in the multilayerin the present embodiment, a high reflectivity of 50% or more can beobtained for the EUV ray in a wide incidence range (at least anincidence angle of 18° to 25°). Particularly, in a region A1 (anincidence angle range of θ1 (18.4°) to θ2 (24.8°) shown in the drawing,the reflectivity is almost constant in the vicinity of 60% and there isalmost no incidence angle dependence of the reflectivity, therefore, ahigh resolution can be obtained.

Embodiment 6

Next, a sixth embodiment of the present invention will be explained. Amultilayer in the present embodiment is one in which the materialconfiguration of each layer and the total film thickness are optimizedwhile the ratio of the film thickness for each layer is maintained so asto be capable of obtaining a high reflectivity for the EUV ray having awavelength of 13.5 nm and being made incident at an incidence angle of0° to 20°. The multilayer in the present embodiment is used, forexample, to obtain a high reflectivity uniformly on the entirereflective surface by controlling the total film thickness for eachsection for optical elements with different light ray incidence anglesfor each section in the same reflective surface.

The multilayer in the present embodiment is one formed by forming themultilayer having the structure shown in the following Table 5 on asynthetic silica glass substrate polished precisely. Note that, thetotal film thickness of the multilayer in the present embodiment isabout 420 nm to 430 nm. Further, it is preferable for the thickness ofeach layer of the multilayer to be not constant and to be adjusted so asto obtain a desired reflectivity by varying the thickness in accordancewith the position on the multilayer.

TABLE 5 A Unit Periodic Structure Number of Reoetitions 1 Ru/Si 4 2Ru/Mo/Si 6 3 Mo/Si 5 4 Ru/Mo/Si 5 5 Mo/Ru/Mo/Si 2 6 Mo/Si 9 7Mo/Ru/Mo/Si 19 8 Mo/Si 3 9 Mo 1

In the following Table 6, Table 7, and Table 8, the film thickness foreach layer of the multilayer in the present embodiment is shown. Notethat, since the number of layers of the multilayer is large, the tableis shown in a plurality of divided tables. According to these tables,the 28th and 69th silicon layers counted from the substrate side are theextremely thick silicon layer.

TABLE 6 More Unit Preferable Film Preferable Periodic Thickness RangeFilm Thickness Structure (nm) (nm)  1 Ru 9~3 6  2 Si 6~2 4  3 Ru 6~2 4 4 Si 6~2 4  5 Ru 6~2 4  6 Si 6~2 4  7 Ru 6~2 4  8 Si 6~2 4  9 Ru 5~2 310 Mo 2~0 1 11 Si 6~2 4 12 Ru 4~1 3 13 Mo 2~0 1 14 Si 6~2 4 15 Ru 4~1 316 Mo 2~0 1 17 Si 6~2 4 18 Ru 4~1 3 19 Mo 2~0 1 20 Si 6~2 4 21 Ru 3~1 222 Mo 2~0 1 23 Si 6~2 4 24 Ru 2~0 1 25 Mo 3~1 2 26 Si 6~2 4 27 Mo 5~2 328 Si 22~7  15 29 Mo 5~2 3 30 Si 6~2 4 31 Mo 5~2 3 32 Si 6~2 4 33 Mo 5~23 34 Si 6~2 4 35 Mo 5~2 3 36 Si 6~2 4 37 Ru 2~0 1 38 Mo 3~1 2 39 Si 6~24 40 Ru 2~0 2 41 Mo 3~1 2 42 Si 6~2 4 43 Ru 2~0 1 44 Mo 3~1 2 45 Si 6~24 46 Ru 2~0 1 47 Mo 3~1 2 48 Si 6~2 4 49 Ru 2~0 1 50 Mo 3~1 2 51 Si 6~24 52 Mo 2~0 1 53 Ru 2~0 1 54 Mo 3~1 2 55 Si 6~2 4 56 Mo 2~0 1 57 Ru 2~01 58 Mo 4~1 2 59 Si 6~2 4 60 Mo 5~2 3 61 Si 7~2 4 62 Mo 4~1 3 63 Si 7~25 64 Mo 4~1 3 65 Si 7~2 5 66 Mo 3~1 2 67 Si 8~3 5

TABLE 7 More Unit Preferable Film Preferable Periodic Thickness FilmThickness Structure Range(nm) (nm) 68 Mo 2~0 1 69 Si 36~12 24 70 Mo 3~12 71 Si 7~2 5 72 Mo 4~1 3 73 Si 6~2 4 74 Mo 5~2 3 75 Si 6~2 4 76 Mo 5~23 77 Si 6~2 4 78 Mo 2~0 1 79 Ru 2~0 1 80 Mo 3~1 2 81 Si 6~2 4 82 Mo 2~01 83 Ru 3~1 2 84 Mo 2~0 2 85 Si 6~2 4 86 Mo 2~0 1 87 Ru 3~1 2 88 Mo 2~01 89 Si 6~2 4 90 Mo 2~0 1 91 Ru 3~1 2 92 Mo 2~0 1 93 Si 6~2 4 94 Mo 2~01 95 Ru 3~1 2 96 Mo 2~0 1 97 Si 6~2 4 98 Mo 2~0 1 99 Ru 3~1 2 100  Mo2~0 1 101  Si 6~2 4 102  Mo 2~0 1 103  Ru 3~1 2 104  Mo 2~0 1 105  Si6~2 4 106  Mo 2~0 1 107  Ru 3~1 2 108  Mo 2~0 1 109  Si 6~2 4 110  Mo2~0 1 111  Ru 3~1 2 112  Mo 2~0 1 113  Si 6~2 4 114  Mo 2~0 1 115  Ru3~1 2 116  Mo 2~0 1 117  Si 6~2 4 118  Mo 2~0 1 119  Ru 3~1 2 120  Mo2~0 1 121  Si 6~2 4 122  Mo 2~0 1 123  Ru 3~1 2 124  Mo 2~0 2 125  Si6~2 4

TABLE 8 Preferable Unit Film Thickness More Preferable Periodic RangeFilm Structure (nm) Thickness (nm) 126 Mo 2~0 1 127 Ru 2~0 2 128 Mo 2~02 129 Si 6~2 4 130 Mo 2~0 1 131 Ru 2~0 1 132 Mo 2~0 2 133 Si 6~2 4 134Mo 2~0 1 135 Ru 2~0 1 136 Mo 3~1 2 137 Si 6~2 4 138 Mo 2~0 1 139 Ru 2~01 140 Mo 3~1 2 141 Si 6~2 4 142 Mo 2~0 1 143 Ru 2~0 1 144 Mo 3~1 2 145Si 6~2 4 146 Mo 2~0 1 147 Ru 2~0 1 148 Mo 3~1 2 149 Si 6~2 4 150 Mo 2~01 151 Ru 2~0 1 152 Mo 3~1 2 153 Si 6~2 4 154 Mo 5~2 3 155 Si 6~2 4 156Mo 5~2 3 157 Si 6~2 4 158 Mo 4~1 3 159 Si 7~1 4 160 Mo 4~1 3

FIG. 11 and FIG. 12 are graphs showing the incidence angle dependence ofthe reflectivity of the multilayer mirror according to the presentembodiment. In the drawing, the horizontal axis represents the incidenceangle (degree (°)) of the light made incident to the multilayer mirrorand the vertical axis represents the reflectivity (%) for the EUV rayhaving a wavelength (λ) of 13.5 nm. The reflectivity shown in each ofFIG. 11 and FIG. 12 is obtained from the multilayer the total filmthickness of which is varied while the ratio of the film thickness ofeach layer of the multilayer is maintained. The film thickness shown ineach drawing is a value when the total film thickness of the multilayerin FIG. 11(A) is assumed to be 1.000 and is varied at an interval of0.0025 in the range of 1.000 (FIG. 11(A)) to 0.9650 (FIG. 12(G)).

A region A2 sandwiched by the two longitudinal dotted lines in eachdrawing shows an incidence angle range in which the incidence angledependence of the reflectivity is small. As seen from FIG. 11 and FIG.12, as the total film thickness increases, the region A2 shifts towardlarger incidence angles (to the right in the drawing). For example,while the region A2 in FIG. 12(G) is in the range of the incidence angleof about 4° to about 9°, in FIG. 11(A), the range is between about 17°and 20°. Therefore, according to the present embodiment, by varying thetotal film thickness of the multilayer, a high reflectivity of 50% ormore can be obtained in a wide range of the incidence angle of 0° to20°.

Embodiment 7

Next a seventh embodiment of the present invention will be explained. Inthe multilayer in the present embodiment, the material configuration andthe film thickness of each layer are optimized so as to be capable ofobtaining a high reflectivity for the EUV ray having a wavelength of13.5 nm across the entire incidence light range from 0° to 20°. Themultilayer in the present embodiment is one formed by forming themultilayer having a structure shown in the following Table 9 on asynthetic silica glass substrate precisely polished. Note that, thetotal film thickness of the multilayer in the present embodiment isabout 280 nm. Further, it is preferable for the thickness of each layerof the multilayer to be not constant and to be adjusted so as to obtaina desired reflectivity by varying in accordance with the position on themultilayer.

TABLE 9 A Unit Periodic Structure Number of Repetitions 1 Mo/Ru/Mo/Si 32 Ru/Mo/Si 2 3 Mo/Ru/Mo/Si 1 4 Ru/Mo/Si 5 5 Mo/Si 3 6 Mo/Ru/Mo/Si 4 7Ru/Mo/Si 1 8 Mo/Ru/Mo/Si 1 9 Mo/Si 3 10 Mo/Ru/Mo/Si 2 11 Ru/Mo/Si 1 12Mo/Ru/Mo/Si 10 13 Mo/Si 1 14 Mo 1

FIG. 13 is a graph showing the incidence angle dependence of thereflectivity of the multilayer mirror according to the presentembodiment. In the drawing, the horizontal axis represents the incidenceangle (degree (°)) of light made incident to the multilayer mirror andthe vertical axis represents the reflectivity (%) for the EUV ray havinga wavelength (λ) of 13.5 nm. As seen from the drawing, according to themultilayer mirror in the present embodiment, a high reflectivity of 45%or more (in more detail, 54% or more) can be obtained across the entireincidence angle range of 0° to 20°.

Embodiment 8

Next an eighth embodiment of the present invention will be explained. Inthe multilayer in the present embodiment, the material configuration andthe film thickness of each layer are optimized so as to be capable ofobtaining a high reflectivity for the EUV ray (Extreme Ultra-Violet ray)having a wavelength of 13.1 nm to 13.9 nm and being made incidentvertically. The multilayer in the present embodiment is one formed byforming the multilayer having a structure shown in the following Table10 on a synthetic silica glass substrate precisely polished. Note that,the total film thickness of the multilayer in the present embodiment isabout 360 nm. Further, it is preferable for the thickness of each layerof the multilayer to be not constant and to be adjusted so as to obtaina desired reflectivity by varying in accordance with the position on themultilayer.

TABLE 10 A Unit Periodic Structure Number of Repetitions 1 Ru/Si 1 2Ru/Mo/Si 1 3 Ru/Si 1 4 Mo/Si 2 5 Ru/Si 1 6 Ru/Mo/Si 5 7 Mo/Si 3 8Ru/Mo/Si 5 9 Mo/Si 5 10 Ru/Mo/Si 4 11 Mo/Si 4 12 Ru/Mo/Si 12 13Mo/Ru/Mo/Si 2 14 Mo/Si 1 15 Mo 1

In the following Table 11 and Table 12, the film thickness for eachlayer of the multilayer in the present embodiment is shown. Note that,since the number of layers of the multilayer is large, the table isshown in a plurality of divided tables. According to these tables, the28th, the 51th, the 73th, and 75th silicon layers counted from thesubstrate side are the extremely thick silicon layer.

TABLE 11 Preferable More Unit Film Thickness Preferable Periodic RangeFilm Thickness Structure (nm) (nm) 1 Ru 6~2 4 2 Si 5~2 3 3 Ru 5~2 3 4 Mo2~0 1 5 Si 5~2 3 6 Ru 5~2 4 7 Si 6~2 4 8 Mo 8~3 6 9 Si 7~2 5 10 Mo 6~2 411 Si 5~2 3 12 Ru 5~2 3 13 Si 5~2 4 14 Ru 4~1 3 15 Mo 2~0 1 16 Si 5~2 417 Ru 4~1 3 18 Mo 2~0 1 19 Si 5~2 4 20 Ru 3~1 2 21 Mo 2~0 2 22 Si 5~2 423 Ru 2~0 2 24 Mo 3~1 2 25 Si 5~2 4 26 Ru 2~0 1 27 Mo 4~1 2 28 Si 12~4 8 29 Mo 2~0 1 30 Si 6~2 4 31 Mo 5~2 3 32 Si 5~2 4 33 Mo 5~2 3 34 Si 6~24 35 Ru 2~0 1 36 Mo 3~1 2 37 Si 6~2 4 38 Ru 2~0 2 39 Mo 3~1 2 40 Si 6~24 41 Ru 2~0 1 42 Mo 3~1 2 43 Si 6~2 4 44 Ru 2~0 1 45 Mo 3~1 2 46 Si 6~24 47 Ru 2~0 1 48 Mo 4~1 2 49 Si 6~2 4 50 Mo 4~1 3 51 Si 24~8  16 52 Mo2~0 1 53 Si 7~2 4 54 Mo 5~2 3 55 Si 5~2 4 56 Mo 5~2 3 57 Ru 5~2 4 58 Mo5~2 4 59 Si 6~2 4 60 Ru 2~0 1 61 Mo 3~1 2 62 Si 6~2 4 63 Ru 2~0 1 64 Mo3~1 2 65 Si 6~2 4 66 Ru 2~0 1 67 Mo 3~1 2 68 Si 6~2 4

TABLE 12 Preferable More Unit Film Thickness Preferable Periodic RangeFilm Thickness Structure (nm) (nm) 69 Ru 2~0 1 70 Mo 4~1 2 71 Si 6~2 472 Mo 4~1 3 73 Si 18~6  12 74 Mo 2~0 1 75 Si 15~5  10 76 Mo 4~1 3 77 Si6~2 4 78 Mo 5~2 3 79 Si 6~2 4 80 Ru 2~0 1 81 Mo 3~1 2 82 Si 6~2 4 83 Ru3~1 2 84 Mo 2~0 1 85 Si 6~2 4 86 Ru 3~1 2 87 Mo 2~0 1 88 Si 5~2 4 89 Ru3~1 2 90 Mo 2~0 1 91 Si 5~2 4 92 Ru 3~1 2 93 Mo 2~0 1 94 Si 5~2 4 95 Ru3~1 2 96 Mo 2~0 1 97 Si 6~2 4 98 Ru 3~1 2 99 Mo 2~0 1 100  Si 6~2 4 101 Ru 3~1 2 102  Mo 2~0 1 103  Si 6~2 4 104  Ru 3~1 2 105  Mo 2~0 1 106  Si6~2 4 107  Ru 3~1 2 108  Mo 2~0 1 109  Si 6~2 4 110  Ru 3~1 2 111  Mo2~0 1 112  Si 6~2 4 113  Ru 3~1 2 114  Mo 2~0 1 115  Si 6~2 4 116  Mo2~0 1 117  Ru 2~0 2 118  Mo 2~0 1 119  Si 6~2 4 120  Mo 2~0 1 121  Ru2~0 1 122  Mo 2~0 1 123  Si 6~2 4 124  Mo 4~1 3 125  Si 6~2 4 126  Mo4~1 3

FIG. 14 is a graph showing the spectral reflectivity properties of themultilayer mirror according to the present embodiment. In the drawing,the horizontal axis represents the wavelength (nm) of incidence lightand the vertical axis represents the reflectivity (%). Note that, it isassumed that the incidence angle of light is 0° (vertical incidence onthe reflective surface). As seen from the drawing, according to themultilayer mirror in the present embodiment, a high reflectivity of 45%or more (in more detail, 50% or more) can be obtained across the entirewide wavelength range described above.

Embodiment 9

Next a ninth embodiment of the present invention will be explained. Inthe multilayer in the present embodiment, the material configuration andthe film thickness of each layer are optimized so as to be capable ofobtaining a reflectivity as high as possible for the EUV ray having awavelength of 13.5 nm and being made incident vertically. The multilayerin the present embodiment is one formed by forming the multilayer havinga structure shown in the following Table 13 on a synthetic silica glasssubstrate precisely polished. Note that, the total film thickness of themultilayer in the present embodiment is about 510 nm. Further, it ispreferable for the thickness of each layer of the multilayer to be notconstant and to be adjusted so as to obtain a desired reflectivity byvarying it in accordance with the position on the multilayer.

TABLE 13 A Unit Periodic Structure Number of Repetitions 1 Si 1 2 Ru/Si17 3 Ru/Mo/Si 56 4 Ru/Mo 1

FIG. 15 is a graph showing the spectral reflectivity properties of themultilayer mirror according to the present embodiment. In the drawing,the horizontal axis represents the wavelength (nm) of incidence lightand the vertical axis represents the reflectivity (%). Note that, it isassumed that the incidence angle is 0° (vertical incidence on thereflective surface). As seen from the drawing, according to themultilayer mirror in the present embodiment, a high reflectivity of 70%or more (for example, about 76%), which is higher than that in FIG. 20described above, can be obtained for the EUV ray having a wavelength of13.5 nm.

Embodiment 10

Next a tenth embodiment of the present invention will be explained. Inthe multilayer in the present embodiment, the material configuration andthe film thickness of each layer are optimized so as to be capable ofobtaining a high reflectivity for the EUV ray (Extreme Ultra-Violet ray)having a wavelength of 13.5 nm to 14.2 nm at the time of verticalincidence. The multilayer in the present embodiment is a Mo/Simultilayer in which a molybdenum layer (a low refractive-index film) anda silicon layer (a high refractive-index film) are laminated by turns ona synthetic silica glass substrate precisely polished.

Note that, the total film thickness of the multilayer in the presentembodiment is about 330 nm. Further, it is preferable for the thicknessof each layer of the multilayer to be not constant and to be adjusted soas to obtain a desired reflectivity by varying in accordance with theposition on the multilayer. In the following Table 14 and Table 15, thefilm thickness for each layer of the multilayer in the presentembodiment is shown. Note that, since the number of layers of themultilayer is large, the table is shown in a plurality of dividedtables. According to these tables, the 46th silicon layer (the siliconlayer located almost in the middle in the multilayer) is the extremelythick silicon layer.

TABLE 14 Preferable Film More Unit Thickness Preferable Periodic RangeFilm Thickness Structure (nm) (nm)  1 Mo 20~5  11  2 Si 6~2 4  3 Mo 6~24  4 Si 6~2 4  5 Mo 6~2 4  6 Si 6~2 3  7 Mo 9~3 6  8 Si 8~3 5  9 Mo 7~24 10 Si 6~2 3 11 Mo 6~2 4 12 Si 6~2 4 13 Mo 6~2 4 14 Si 6~2 4 15 Mo 6~24 16 Si 6~2 4 17 Mo 6~2 4 18 Si 6~2 4 19 Mo 6~2 4 20 Si 6~2 4 21 Mo 6~24 22 Si 6~2 4 23 Mo 6~2 3 24 Si 6~2 4 25 Mo 12~3  7 26 Si 6~2 4 27 Mo6~2 3 28 Si 6~2 4 29 Mo 6~2 4 30 Si 6~2 4 31 Mo 6~2 4 32 Si 6~2 4 33 Mo6~2 4 34 Si 6~2 4 35 Mo 6~2 4 36 Si 6~2 4 37 Mo 6~2 4 38 Si 6~2 4 39 Mo6~2 3 40 Si 6~2 4 41 Mo 6~2 3 42 Si 6~2 4 43 Mo 6~2 3 44 Si 8~2 5

TABLE 15 More Unit Preferable Film Preferable Periodic Thickness RangeFilm Thickness Structure (nm) (nm) 45 Mo 2~0 1 46 Si 14~6  7 47 Mo 6~2 348 Si 6~2 4 49 Mo 6~2 3 50 Si 6~2 4 51 Mo 6~2 4 52 Si 6~2 4 53 Mo 6~2 454 Si 6~2 4 55 Mo 6~2 4 56 Si 6~2 4 57 Mo 6~2 4 58 Si 6~2 4 59 Mo 6~2 460 Si 6~2 4 61 Mo 6~2 4 62 Si 6~2 4 63 Mo 6~2 4 64 Si 6~2 4 65 Mo 6~2 466 Si 6~2 4 67 Mo 6~2 3 68 Si 6~2 4 69 Mo 6~2 3 70 Si 6~2 4 71 Mo 6~2 372 Si 6~2 4 73 Mo 6~2 3 74 Si 6~2 4 75 Mo 6~2 3 76 Si 6~2 4 77 Mo 6~2 378 Si 6~2 4 79 Mo 6~2 3 80 Si 6~2 4 81 Mo 6~2 3 82 Si 7~2 4 83 Mo 6~2 384 Si 6~2 4 85 Mo 5~1 3 86 Si 6~2 3

FIG. 16 is a graph showing the spectral reflectivity properties of themultilayer mirror according to the present embodiment. Note that, themethod for forming the multilayer uses ion beam sputtering. In thedrawing, the horizontal axis represents the wavelength (nm) of incidencelight and the vertical axis represents the reflectivity (O). It isassumed that the incidence angle of light is 0° (vertical incidence onthe reflective surface). The solid line in FIG. 16 shows the wavelengthproperties of the reflectivity when the film is formed using asputtering gas and an argon (Ar) gas and the dotted line shows thewavelength properties of the reflectivity when the film is formed usinga krypton (Kr) gas as a sputtering gas.

As seen from FIG. 16, according to the multilayer mirror in the presentembodiment, a high reflectivity of 45% or more can be obtained acrossthe wide wavelength range described above. Further, when the film isformed using a Kr gas as shown by the dotted line, the reflectivity peakis larger and the full width at half maximum of the spectralreflectivity is wider than the case where the film is formed using an Argas as shown by the solid line.

FIG. 17 is a graph showing the incidence angle dependence of thereflectivity of the multilayer mirror according to the presentembodiment. In the drawing, the horizontal axis represents the incidenceangle (degree (°)) of light made incident to the multilayer mirror andthe vertical axis represents the reflectivity (%) for the EUV ray havinga wavelength (λ) of 13.5 nm. As seen from the drawing, according to themultilayer mirror in the present embodiment, a high reflectivity of 45%or more (more preferably, 50% or more) can be obtained across the entirewide incidence angle range of 0° to 20°.

Embodiment 11

FIG. 18 is a schematic diagram of exposure equipment according to anembodiment of the present invention. As shown schematically, EUVexposure 100 has an X-ray generation device (a laser plasma X-raysource) 101. The X-ray generation device 101 has a spherical vacuumcontainer 102 and the interior of the vacuum container 102 is evacuatedby a vacuum pump. At the upper side inside the vacuum container 102 inthe drawing, a multilayer paraboloidal mirror 104 is arranged itsreflective surface 104 a facing downward (in the +Z direction) in thedrawing.

On the right-hand side of the vacuum container 102 in the drawing, alens 106 is arranged and to the right of the lens 106, a laser lightsource, not shown in the drawing, is arranged. The laser light sourceemits pulse laser light 105 in the −Y direction. The pulse laser light105 converges on the focal point of the multilayer paraboloidal mirrorby the lens 106. At the focal point, a target material (xenon (Xe) etc.)is arranged and when the target material 103 is irradiated with thepulse laser light 105 caused to converge, a plasma 107 is generated. Theplasma 107 emits a soft X-ray (EUV ray) 108 in a wavelength band near 13nm.

At lower part of the vacuum container 102, an X-ray filter 109 forcutting visible light is provided. The EUV ray 108 is reflected in the+Z direction by the multilayer paraboloidal mirror 104, passes throughthe X-ray filter 109 and is guided to an exposure chamber 110. At thistime, the visible light spectrum band of the EUV ray 18 is cut.

Note that, a xenon gas is used as a target material in the presentembodiment, however, a xenon cluster or liquid drop may be used and asubstance such as tin (Sn) may also be used. Further, a laser plasmaX-ray source is used as the X-ray generation device 101, however, adischarge plasma X-ray source may be adopted. A discharge plasma X-raysource turns a target material into plasma by discharge of a high pulsevoltage and causes X-rays to emit from the plasma.

Under the X-ray generation device 101 in the drawing, the exposurechamber 110 is provided. Inside the exposure chamber 110, anillumination optical system 113 is arranged.

The illumination optical system 113 consists of a condenser systemmirror, a fly eye optical system mirror, etc. (shown in a simplifiedshape in the drawing), and forms the EUV ray 108 made incident from theX-ray generation device 101 into a circular shape and emits it leftwardin the drawing.

On the left-hand side of the illumination optical system 113, a mirror115 is arranged. The mirror 115 is a circular concave mirror and heldvertically (parallel to the Z-axis) by a holding member, not shown, sothat the reflective surface 115 a faces rightward (in the +Y direction)in the drawing. On the right-hand side of the mirror 115 in the drawing,an optical path bending mirror 116 is arranged. Above the optical pathbending mirror 116 in the drawing, a reflective type mask 111 isarranged horizontally (parallel to the XY plane) so that the reflectivesurface 111 a faces downward (in the +Z direction). After reflected andcaused to converge by the mirror 115, the EUV ray emitted from theillumination optical system 113 reaches the reflective surface 111 a ofthe reflective type mask 111 via the optical path bending mirror 116.

The mirrors 115 and 116 are composed of substrates made of low thermalexpansion glass with slight thermal deformation, the reflective surfaceof which has been processed highly precisely. On the reflective surface115 a of the mirror 115, a reflective multilayer in which a highrefractive-index film and low refractive-index film are laminated byturns is formed like the reflective surface of the multilayerparaboloidal mirror. Note that, when an X-ray having a wavelength of 10to 15 nm is used, a reflective multilayer may be used, which is acombination of a substance such as molybdenum (Mo), ruthenium (Ru), andrhodium (Rh) and a substance such as silicon (Si), beryllium (Be), andcarbon tetraboride (B₄C).

Also on the reflective surface 111 a of the reflective type mask 111, areflecting film composed of a multilayer is formed. On the reflectingfilm of the reflective type mask 111, a mask pattern in accordance witha pattern to be transferred onto a wafer 112 is formed. The reflectivetype mask 111 is attached to a mask stage 111 shown at the upper part inthe drawing. The mask stage 117 is capable of moving at least in the Ydirection and the EUV ray reflected by the optical path bending mirror116 is scanned sequentially on the reflective type mask 111.

Down the reflective mask 111 in the drawing, a projection optical system114 and a wafer (a substrate applied with a sensitive resin) 112 arearranged in this order from above. The projection optical system 114 iscomposed of a plurality of mirrors etc. The wafer 112 is fixed on thewafer stage 118 capable of moving in the XYZ directions so that theexposure surface 1112 a faces upward (in the −Z direction) in thedrawing. The EUV ray reflected by the reflective type mask 111 isreduced by the projection optical system with a predetermined reductionfactor (for example, ¼) and forms an image on the wafer 112 and thepattern on the mask 111 is transferred onto the wafer 112.

On the mirror (excluding the grazing incidence mirror making use of thetotal reflection) used in the exposure equipment 100 in the presentembodiment, a multilayer having any one of structures described in thefirst to tenth embodiments described above is formed. Note that, themultilayer paraboloidal mirror 104, the mirrors in the illuminationoptical system 113 and the projection optical system 114, etc., areprovided with a cooling mechanism, not shown in the drawing, in order toprevent the surface temperature from exceeding 100° C.

Since the incidence light of the EUV ray to the reflective surface ofthe multilayer paraboloidal mirror 104 considerably varies according tothe position on the plane, the periodic length also varies considerablyin the plane. As described above, a slight error occurs in thedistribution of the periodic length of the multilayer paraboloidalmirror 104 and in the substrate mounting position, therefore, thereflectivity varies due to the error between the incidence anglesupposed at the time of the control of the periodic length and theactual incidence angle. According to the present embodiment, such achange in the reflectivity seldom occurs by using a multilayer mirrorhaving a wide full width at half maximum of the reflectivity accordingto the above-mentioned embodiments. Further, by using a multilayerhaving a wide reflection band as the multilayer mirror constituting theillumination optical system 113 and the projection optical system 114,the image forming performance of the optical system can be maintainedhigh, therefore, it is possible to uniformalize the illuminance on theimage forming surface and the amount of light in the pupil and anexcellent resolution can be obtained.

In the present embodiment, the multilayer paraboloidal mirror 104 etc.is cooled, however, if cooling cannot be performed sufficiently, it mayalso possible to add an additional layer such as that in the second tofourth embodiments into the structure by making use of the filmconfiguration (Mo/SiC/Si, MoC/Si multilayers etc.) the reflectivity ofwhich drops slightly even if the temperature increases.

Supplemental Description

Hereinafter, supplemental description on the above-mentioned embodimentswill be made.

FIG. 22(A) is a graph showing the incidence wavelength properties of thetheoretical reflectivity of the Mo/Si multilayer and the Ru/Simultilayer. In the drawing, the horizontal axis represents thewavelength of incidence light and the vertical axis represents thetheoretical reflectivity (the calculated value of the reflectivity). Thesolid line in the drawing shows the theoretical reflectivity of theMo/Si multilayer of 100 pair layers and the dotted line shows thetheoretical reflectivity of the Ru/Si multilayer of 100 pair layers. Asseen from FIG. 22(A), the full width at half maximum of the Mo/Simultilayer having a sufficiently large number of pairs of formed layersas many as 100 pair layers is 0.6 nm and the full width at half maximumof the Ru/Si multilayer is 0.8 nm.

FIG. 22(B) is a graph showing the change in the full width at halfmaximum and the peak reflectivity with respect to the number of pairs offormed layers of the Mo/Si multilayer in the multilayer configured byforming the Mo/Si multilayer on the Ru/Si multilayer. In the drawing,the horizontal axis represents the number of pair layers of the Mo/Simultilayer formed on the Ru/Si multilayer of 100 pair layers. The fullwidth at half maximum with respect to the number of pair layers of theMo/Si multilayer is expressed by a white triangle (Δ) and the peak valueof the reflectivity (the peak reflectivity) is expressed by a blackcircle ().

As seen from FIG. 22(B), as the number of pair layers of the Mo/Simultilayer increases, the peak reflectivity increases, however, italmost saturates when the number becomes 15 pair layers or more. On theother hand, the full width at half maximum decreases as the number ofpair layers of the Mo/Si multilayer increases. Then, when the number ofpair layers of the Mo/Si multilayer becomes 15 pair layers, it fallsbelow 0.7 nm and approaches the value of the Mo/Si multilayer (refer toFIG. 22(A)).

As described above, it is preferable for the number of pairs of formedlayers of the Mo/Si multilayer to be two pair layers or more in order toobtain the effect of the increase in the reflectivity and to keep theinfluence of the decrease in the full width at half maximum to aminimum, and it is more preferable to be five to ten pair layers.

As seen from FIG. 23, in the case of the dotted line (ii) and the chainline (iii), the top part is not so flat but in the case of the solidline (i), the top part of the reflectivity peak is significantly flat.It is apparent from this that setting the thickness of the additionallayer to about half the periodic length of the multilayer is effectiveto reduce the change in the reflectivity near the peak.

Half the periodic length of the multilayer means half the opticalthickness (film thickness×refractive index) of one period in theperiodic structural part in the multilayer. It is preferable for thethickness of the additional layer to be half the optical thickness,however, it is not necessary to be strictly half the optical thicknessas described above, and it is only necessary to have substantially thethickness. Therefore, it is preferable for the difference between thethickness of the additional layer and half the optical thickness to bewithin 5/100 of the wavelength of EUV ray to be utilized, and morepreferable to be within 3/100 of the utilized wavelength.

The optical thickness of one period in the multilayer structure is abouthalf the wavelength of incidence light, therefore, in other words, it isnecessary to set the optical thickness of an additional layer to aboutone-fourth of the utilized wavelength. Note that, as the angle (theangle of refraction) that the transmitted EUV ray makes with the normalto the boundary surface increases, the optical path length in the unitperiodic structure becomes longer than the film thickness (if the angleof refraction is assumed to be 0, the optical path length=filmthickness/cos θ). Therefore, it is necessary to adjust the thickness ofthe additional layer in accordance with the incidence angle of EUV rayat the time of use. When the utilized wavelength is, for example, 13.5nm, it is preferable for the thickness of the additional layer to be inthe range of half the periodic length of the multilayer ±0.68 nm and atthe time of the use in the incidence angle range of 5° to 10°, it ispreferable to be within the range of 3.4±0.68 nm.

Additionally, the configuration of the multilayer according to thepresent invention is used for infrared, visible, and ultraviolet ray,and it can also be thought to somewhat resemble an Etalon in which aspace having a thickness of one-fourth of the used wavelength is addedbetween reflecting films. However, the multilayer according to thepresent invention quite differs from the Etalon in the configuration,purposes of use, and characteristics as described below. The etalon,which is a kind of Fabry-Perot type resonator, is used mainly as anarrow band filter.

FIG. 24 is a schematic diagram of a structure of an Etalon. An Etalon300 is a device that makes use of a multiple interference and has astructure in which two high reflectivity mirrors 301 are arranged so asto sandwich in between a spacer 302 having a certain thickness. Most oflight 303 made incident to the Etalon 300 (the arrow on the left-handside) is reflected to the left side in the drawing to become reflectedlight 305. On the other hand, the two mirrors 301 and the space 302 playa role as a resonator and cause only the light having the wavelengthmeeting the resonance condition among the incidence light 303 to passthrough as transmitted light 304.

Because of this, a sharp transmittance peak occurs. Since the Etalon 300causes only the light having the wavelength meeting the resonancecondition to pass through as described above, the reflectivity fallsonly in the vicinity of the wavelength and the high reflectivity ismaintained at the other wavelengths. Therefore, the spectralreflectivity properties of the Etalon 300 have a sharp valley. Notethat, the Etalon 300 is used as a narrow band filter, the reflectivityof the two reflective surfaces must be high and almost equal.

In contrast to this, in the case of the multilayer of the presentinvention, the reflectivity of the multilayers above and under theadditional layer must not be equal and it is necessary for thereflectivity of the multilayer on the substrate side to be low. If thereflectivity of the multilayer on the substrate side is equal to that ofthe multilayer on the surface side, the drop in the reflectivity due tointerference occurs in a narrow wavelength region and there appears asharp valley near the peak top, therefore, it is no longer a wide bandmultilayer.

As disclosed in the non-patent document 3, it is possible for amultilayer having a structure in which layers with various periodiclengths are laminated to obtain a relatively high reflectivity in a wideband. However, in this case, it is difficult to evaluate the structure.In general, as a method for evaluating the structure of a multilayer, amethod is used in which a small angle scattering of X-ray is performedand the period is evaluated from the detected peak angle.

FIG. 25 is a graph showing a diffraction peak shape expected when theX-ray diffraction intensity angle distribution is varied. FIG. 25(A)shows a diffraction peak shape of a periodically structured multilayer,FIG. 25(B) shows a diffraction peak shape of an uneven periodicstructure, and FIG. 25(C) shows a diffraction peak shape of a multilayerincluding an additional layer (in this example, a silicon layer). In thedrawing, the horizontal axis represents the incidence angle of incidencelight and the vertical axis represents the reflectivity.

As shown in FIG. 25(A), in the case of the multilayer having a periodicstructure, peaks corresponding to the incident angles appear sharply. Onthe other hand, in the case where the periodic length is uneven as anuneven periodic multilayer reported as a wide band multilayer (refer tothe non-patent document 3), as shown in FIG. 25(B), manyirregular-shaped peaks appear and the evaluation of the periodic lengthof the multilayer is difficult.

In contrast to this, according to the present invention, only anadditional layer is added to the periodic structure of the multilayerand sharp diffraction light peaks occur as shown in FIG. 25(C), whichmakes the evaluation of the multilayer periodic length easy. Note that,it is not possible to directly measure the thickness of the additionallayer, however, it is possible to control the thickness of theadditional layer according to the present invention. Specifically, it ispossible to control the thickness of the additional layer by adjustingthe time required for film formation based on the thickness of the filmformed from a substance for the additional layer per a unit time (filmforming rate) in the film forming work, which is obtained from theperiodic length evaluation of the periodically structured part of themultilayer and the time required for film formation.

Also, in the present invention, the number of pair layers of the deeplayer film group is half or less than the number of pair layers of thesurface layer film group. As described above, when the multilayer isnearer to the substrate side than to the additional layer, thereflectivity in the vicinity of the reflectivity peak drops compared tothat when only the surface layer film group is present. Here, since thenumber of pair layers of the deep layer film group is half or less thanthat of the surface layer film group, the amount of drop in thereflectivity is small, the shape of the reflectivity peak is such thatthe front end part is flattened or becomes slightly hollow. It isunlikely that the portion in the vicinity of the reflectivity peak valuebecomes a sharp and deep valley.

FIG. 26 is a graph showing the change in the reflectivity peak shape ofa Mo/Si multilayer when the number of pairs of the deep layer film groupis varied. In the drawing, the horizontal axis represents the wavelengthof incidence light and the vertical axis represents the reflectivity. Inthe example in FIG. 26, the additional layer is silicon. The solid line(i), the chain line (ii), and the dotted line (iii) in the drawing showthe reflectivity when the deep layer film group is a four-pair layer, atwo-pair layer, and a 12-pair layer, respectively, and each of thesurface layer film groups is a 20-pair layer.

As seen from FIG. 26, in the case (ii) where the deep layer film groupis a two-pair layer for the 20-pair layer of the surface layer filmgroup, the reflectivity peak is not sufficiently flattened but remainspointed, however, in the case (i) where the number of pair layers of thedeep layer film group is increased to a four-pair layer, thereflectivity peak is flattened. Further, in the case (iii) where thedeep layer film group is increased to a 12-pair layer, a deep valley isformed on the top of the reflectivity peak and a flat shape cannot beobtained. Hence, it is preferable for the number of pair layers of thedeep layer film group to be at least half or less than the number ofpair layers of the surface layer film group. As described above,according to the present invention, a reflectivity peak the full widthat half maximum of which is wide and the peak of which is flat can beobtained.

According to the present embodiment, the EUV ray wavelength having arelatively high EUV ray reflectivity means that the wavelength is withina range including the maximum value of the reflectivity and the flatportion (the reflectivity is almost constant) of a graph in which thehorizontal axis represents the wavelength and the vertical axisrepresents the reflectivity. For example, in the case of the solid line(i) in FIG. 26 described above, the range is one in which the wavelengthis about 13.2 to about 13.6 nm. It is preferable for a wavelength rangeincluding a desired wavelength (for example, 13.5 nm) to be within 0.5nm, or more preferably within 0.60 nm, in which the reflectivity is 50%or more, and in which the reflectivity peak has a flat shape (thefluctuation in the reflectivity is within ±5%).

Here, the incidence angle having a relatively high EUV ray reflectivitymeans that the angle is within a range including the maximum value ofthe reflectivity and the flat portion (the reflectivity is almostconstant) of a graph in which the horizontal axis represents theincidence angle and the vertical axis represents the reflectivity.

The invention is not limited to the above embodiments and variousmodifications may be made without departing from the spirit and scope ofthe invention. Any improvement may be made in part or all of thecomponents.

1. A multilayer mirror comprising a reflective multilayer in which ahigh refractive-index film and a low refractive-index film are laminatedon a substrate by turns under a condition that a Bragg's reflectioncondition holds that reflected light from a plurality of boundarysurfaces of the high refractive-index film and low-refractive index filmfor EUV ray is put in phase, comprising: an interposed layer having athickness of half or more of a center wavelength of the EUV ray, whereina band of EUV ray wavelength or incidence angle having a relatively highEUV ray reflectively is widened.
 2. The multilayer mirror according toclaim 1, wherein part of layer pairs of the high refractive-index filmand low refractive-index film is composed of two kinds of substances andanother part thereof is composed of three or more kinds of substances.3. The multilayer mirror according to claim 1, wherein each layer islaminated while the film thickness thereof is varied arbitrarily so thatreflectivity for light having a wavelength of 13.1 nm to 13.9 nm is setto 45% or more.
 4. The multilayer mirror according to claim 1, whereinthe interposed layer is at least one layer of the high refractive-indexfilm.
 5. Exposure equipment which forms a pattern by selectivelyirradiating a sensitive substrate with EUV ray, comprising themultilayer mirror according to claim 1 in an optical system.